High refractive index addition-fragmentation agents

ABSTRACT

Addition-fragmentation agents having the following functional groups: 1) a labile addition-fragmentation group that can cleave and reform to relieve strain, 2) at least one high refractive index group, and 3) at least one ethylenically unsaturated, polymerizable group are described.

BACKGROUND

The present disclosure provides novel addition-fragmentation agents foruse in low-stress polymerizable compositions. Free-radicalpolymerization is typically accompanied by a reduction in volume asmonomers are converted to polymer. The volumetric shrinkage producesstress in the cured composition, leading to a microcracks anddeformation. Stress transferred to an interface between the curedcomposition and a substrate can cause failure in adhesion and can affectthe durability of the cured composition.

The addition-fragmentation agents of this disclosure provide stressrelief by including labile linkages that can cleave and reform duringthe polymerization process. Such cleavage may provide a mechanism toallow for network reorganization, relieve polymerization stress, andprevent the development of high stress regions. The instantaddition-fragmentation agents may further provide stress relief bydelaying the gel point, the point at which the polymerizable compositiontransitions from a viscous material to an elastic or viscoelastic solid.The longer the polymerizable mixture remains viscous, the more timeavailable during which material flow can act to alleviate stress duringthe polymerization process.

The addition-fragmentation agents provide novel stress-reducing agentsthat have application in dental compositions, thin films, hardcoats,composites, adhesives, and other uses subject to stress reduction.

SUMMARY

The present disclosure provides addition-fragmentation agents having thefollowing functional groups: 1) a labile addition-fragmentation groupthat can cleave and reform to relieve strain, 2) at least one highrefractive index group, and 3) at least one ethylenically unsaturated,polymerizable group.

When added to a mixture of polymerizable monomers, the high refractiveindex groups of the agent may increase the refractive index of theresulting polymer. In addition, it has been observed that incorporationof high refractive index groups increases the depth of cure during a UVinitiated polymerization process, by reducing light-scattering due tomismatched refractive indices.

The addition-fragmentation agents may be added to polymerizable monomermixtures to reduce the polymerization-induced stresses. This disclosurefurther provides a method of preparing the addition-fragmentation agentsof formula I, as further disclosed herein.

This disclosure further provides a curable composition comprising theaddition-fragmentation agent and one or more free-radicallypolymerizable monomers or oligomers, the addition-fragmentation agentproviding a reduction in stress of the resultant polymers. Theaddition-fragmentation agents act as chain-transfer agents via anaddition-fragmentation process whereby the addition-fragmentationlinkages are labile during polymerization and continuously cleave andreform, providing a reduction in polymerization-based stress.

In some embodiments, the addition-fragmentation agent comprises two ormore ethylenically unsaturated polymerizable groups, so that the agentfunctions as a labile crosslinking agent in polymerizable compositions.Labile crosslinks may provide a mechanism to allow for networkreorganization, relieve polymerization stress, and prevent thedevelopment of high stress regions. The instant crosslinking agent mayfurther provide stress relief by delaying the gel point, the point atwhich the polymerizable composition transitions from a viscous materialto a viscoelastic solid. The longer the polymerizable mixture remainsviscous, the more time available during which material flow can act toalleviate stress during the polymerization process.

As used herein:

“acryloyl” is used in a generic sense and mean not only derivatives ofacrylic acid, but also amine, and alcohol derivatives, respectively;

“(meth)acryloyl” includes both acryloyl and methacryloyl groups; i.e. isinclusive of both esters and amides.

“curable” means that a coatable material can be transformed into asolid, substantially non-flowing material by means of free-radicalpolymerization, chemical cross linking, radiation crosslinking, or thelike.

“alkyl” includes straight-chained, branched, and cycloalkyl groups andincludes both unsubstituted and substituted alkyl groups. Unlessotherwise indicated, the alkyl groups typically contain from 1 to 20carbon atoms. Examples of “alkyl” as used herein include, but are notlimited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, isobutyl,t-butyl, isopropyl, n-octyl, n-heptyl, ethylhexyl, cyclopentyl,cyclohexyl, cycloheptyl, adamantyl, and norbornyl, and the like. Unlessotherwise noted, alkyl groups may be mono- or polyvalent, i.e.monovalent alkyl or polyvalent alkylene.

“heteroalkyl” includes both straight-chained, branched, and cyclic alkylgroups with one or more heteroatoms independently selected from S, O,and N with both unsubstituted and substituted alkyl groups. Unlessotherwise indicated, the heteroalkyl groups typically contain from 1 to20 carbon atoms. “Heteroalkyl” is a subset of “hydrocarbyl containingone or more S, N, O, P, or Si atoms” described below. Examples of“heteroalkyl” as used herein include, but are not limited to, methoxy,ethoxy, propoxy, 3,6-dioxaheptyl, 3-(trimethylsilyl)-propyl,4-dimethylaminobutyl, and the like. Unless otherwise noted, heteroalkylgroups may be mono- or polyvalent, i.e. monovalent heteroalkyl orpolyvalent heteroalkylene.

“aryl” is an aromatic group containing 5-18 ring atoms and can containoptional fused rings, which may be saturated, unsaturated, or aromatic.Examples of aryl groups include phenyl, naphthyl, biphenyl, phenanthryl,and anthracyl. Heteroaryl is aryl containing 1-3 heteroatoms such asnitrogen, oxygen, or sulfur and can contain fused rings. Some examplesof heteroaryl groups are pyridyl, furanyl, pyrrolyl, thienyl, thiazolyl,oxazolyl, imidazolyl, indolyl, benzofuranyl, and benzthiazolyl. Unlessotherwise noted, aryl and heteroaryl groups may be mono- or polyvalent,i.e. monovalent aryl or polyvalent arylene.

“(hetero)hydrocarbyl” is inclusive of hydrocarbyl alkyl and aryl groups,and heterohydrocarbyl heteroalkyl and heteroaryl groups, the lattercomprising one or more catenary (in-chain) oxygen heteroatoms such asether or amino groups. Heterohydrocarbyl may optionally contain one ormore catenary (in-chain) functional groups including ester, amide, urea,urethane, and carbonate functional groups. Unless otherwise indicated,the non-polymeric (hetero)hydrocarbyl groups typically contain from 1 to60 carbon atoms. Some examples of such heterohydrocarbyls as used hereininclude, but are not limited to, methoxy, ethoxy, propoxy,4-diphenylaminobutyl, 2-(2′-phenoxyethoxy)ethyl, 3,6-dioxaheptyl,3,6-dioxahexyl-6-phenyl, in addition to those described for “alkyl”,“heteroalkyl”, “aryl”, and “heteroaryl” supra.

DETAILED DESCRIPTION

The present disclosure provides addition-fragmentation agents of theformula:

whereinR¹ is each independently a (hetero)alkyl group or a (hetero)aryl group,preferably a C₂-C₁₀ alkylene;Y is —O—. —S—, —O—CO—, O—CO—NH—, —N—CO—, or —NR⁴—, where R⁴ is H orC₁-C₄ alkyl;each X¹ is independently —O— or —NR⁴—, where R⁴ is H or C₁-C₄ alkyl, andn is 0 or 1;m is each independently 1 or 2;R² is alkyl, aryl, a high refractive index group or an ethylenicallyunsaturated, polymerizable group;at least one of said R² groups comprises a high refractive index group;at least one of said R² groups comprises an ethylenically unsaturated,polymerizable group; andsaid addition-fragmentation agent having a refractive index of ≧1.50, asmeasured by an Abbé refractometer.

In some preferred embodiments, at least one, and preferably two or moreof said R¹—Y—R² groups is of the formula:

whereinR⁴ is H or C₁-C₄ alkyl;X¹ is independently —O— or —NR⁴—, where R⁴ is H or C₁-C₄ alkyl; andt is 2 to 10, said —(C_(t)H_(2t))— group optionally substituted by ahydroxy, i.e. —[C_(t)H_(2t)(OH)], such as 2-hydroxypropylene.

More specifically, the addition-fragmentation agent of formula I may berepresented as

whereinR^(RI) comprises a high refractive index group;R^(polmn) comprises an ethylenically unsaturated, polymerizable group;R³² is either R^(RI) or R^(polmn);R³³ is alkyl or aryl, an ethylenically unsaturated polymerizable groupor a high refractive index group;Y is —O—. —S—, —O—CO—, O—CO—NH—, —N—CO—, or —NR⁴—, where R⁴ is H orC₁-C₄ alkyl;each X¹ is independently —O— or —NR⁴, where R⁴ is H or C₁-C₄ alkyl, andn is 0 or 1;each o is independently 1 or 2each p is independently 0 or 1,with the proviso that compound Ia comprises at least one ethylenicallyunsaturated polymerizable group and at least one high refractive indexgroup.

With respect to Formula Ia, it will be appreciated that any of thedepicted R¹ groups may have both an R^(RI) and an R^(polmn) group andthat the compound comprises at least one high refractive index group andat least one ethylenically unsaturated, polymerizable group.

In many applications, such as in compositions for optical or dental use,it is desirable to match the refractive indices of the components,typically the resins and fillers. A mismatch in refractive indices leadsto scattering of light at the interface between the different phases. Asmany applications use high refractive index resins, and correspondinghigh refractive index fillers, it is desirable that additionfragmentation agent have a high refractive index as well. This leads toa better match of the refractive index of the matrix the filler and theaddition-fragmentation agent, leading to a much more opticallytransmissive material. This in turn leads to the ability to provide anindex-matched composition suitable for optical, dental or otherapplications which require optical clarity and minimal haze due toscattering. Further, the high refractive index compositions have betterdepth of cure, as described further herein.

The present disclosure provides stable curable composition that providesenhanced optical translucency. In one embodiment, the present inventionfeatures a hardenable dental composition comprising a dental resin, afiller, and the addition-fragmentation agent. The combined mixture isgenerally within 4 percent of the refractive index of the filler and/orresin, typically within 3 percent thereof, more typically within 1percent thereof, and even more typically within 0.5 percent thereof. Therefractive index of the combined mixture may be measured in the hardenedstate or the unhardened state.

Suitable high refractive index groups are those that will confer arefractive index to the agent of Formula I of at least 1.50. Suitablegroups include, but are not limited to, benzyl, biphenyl, fluorenyl,4-(1-methyl-1-phenethyl)phenoxyethyl; phenylthio; 1-, 2-, 3- and4-napthyl, 1- and 2-naphthylthio; 2,4,6-tribromophenoxy;2,4-dibromophenoxy; 2-bromophenoxy; 1-, and 2-naphthyloxy; 3-phenoxy-;2-, 3- and 4-phenylphenoxy; 2,4-dibromo-6-sec-butylphenyl;2,4-dibromo-6-isopropylphenyl; pentabromobenzyl and pentabromophenyl.

The addition-fragmentation agent of Formula I may be added topolymerizable monomer mixtures to reduce the polymerization-inducedstresses, increase the refractive index of the composition and resultingpolymer, and/or increase the depth cure of mixture. In embodiments wherethe addition-fragmentation agent has two ethylenically unsaturatedgroups, the agent further functions as addition-fragmentationcrosslinking agents, where the crosslinks are labile. This disclosurefurther provides a method of preparing the addition-fragmentation agentsof Formula I, as further disclosed herein.

This disclosure further provides a polymerizable composition comprisingthe addition-fragmentation agent and one or more free-radicallypolymerizable monomers, the addition-fragmentation agent providing areduction in shrinkage and stress of the resultant polymers. Theaddition-fragmentation agents act as chain-transfer agents via anaddition-fragmentation process whereby the crosslinks are labile duringpolymerization and can cleave and reform during the polymerization,providing a reduction in polymerization-based stress.

In some embodiments, the polymerizable composition may be used incoatings, particularly hardcoats, and in dental resins.

It is believed that the addition-fragmentation agent follows an additionfragmentation pathway as shown in the following Scheme 1. In this schemethe addition-fragmentation agent of Formula I is shown in simplifiedform where the —R¹—(Y—R²)_(m) has been abbreviated as R¹⁰, and n=0. Inthe step 1, a free radical species P. adds to the agent. The agent thenfragments as shown in step 2 to form the relatively stable α-carbonyltertiary radical and the α,β-unsaturated ester bearing the residue ofthe free radical species P. This α,β-unsaturated ester can undergoradical addition as shown in step 5. The radical addition may beinitiated by an initiator or a polymer radical.

Concurrently the α-carbonyl tertiary radical can initiate polymerizationof monomer as shown in step 3. For purposes of illustration, amethacrylate monomer is illustrated. On monomer addition, a methacrylateterminated radical intermediate is produced. In the presence of theagent of Formula 1 (as shown in step 4) both addition, andfragmentation, yielding a tertiary radical, occurs.

The bonds between the ethylenically unsaturated groups will form labilebonds. Fragmentation of the addition-fragmentation crosslinking agentprovides a mechanism for crosslink cleavage. The cleavage of labileaddition-fragmentation groups may allow the polymeric network to relaxor reorganize, especially in high stress regions, providing a potentialmechanism for stress relief.

Scheme 1

In general, the compounds of Formula I are prepared by functionalizationof the dimer/trimer of methacrylic acid, or a derivative thereof,whereby the requisite high refractive index group(s) and ethylenicallyunsaturated group(s) are provided.

In one embodiment, the dimer of methacrylic acid or ester thereof may befunctionalized as follows:

where R⁴ is H or C₁-C₄ alkyl,R¹ is each independently a (hetero)alkyl group or a (hetero)aryl group,preferably a C₂-C₁₀ alkylene;each X¹ is independently —O— or —NR⁴—, where R⁴ is H or C₁-C₄ alkyl;R² is alkyl, aryl, a high refractive index group, or an ethylenicallyunsaturated polymerizable group;Y is —O—. —S—, —O—CO—, O—CO—NH—, —N—CO—, or —NR⁴—, where R⁴ is H orC₁-C₄ alkyl;at least one of said R² groups is a high refractive index group;at least one of said R² groups comprises an ethylenically unsaturated,polymerizable group.

In another embodiment, the dimer of methacrylic acid or ester thereofmay be reacted with a polyfunctional compound of the formula:

X⁵ _(m)—R¹—X² _(m),

wherein R¹ is a (hetero)alkyl group or a (hetero)aryl group and X⁵comprises a functional group reactive with the acid or ester functionalgroups (—O—R⁴) of the dimer to form an intermediate of the formula:

and X² is a functional group capable of further functionalization, asdescribed below.

A portion of the X² groups of the intermediate may be reacted with acompound of the formula:

(Z)_(d)—X³,  V

where Z comprises an ethylenically unsaturated polymerizable group, andX³ is a reactive functional group, reactive with the X² groups of theintermediate, and d is at least 1.

A portion of the X² groups of the intermediate may be reacted with acompound of the formula:

(R^(RI))_(d)—X³,  VI

where R^(RI) comprises high refractive index group, and X³ is a reactivefunctional group, reactive with the X² groups of the intermediate.

With respect to the compound of Formulas IV-VI the requisiteethylenically unsaturated group and high refractive index group may beincorporated into the intermediate by means including addition,condensation, substitution and displacement reaction. The ethylenicallyunsaturated moiety, Z, may include, but is not limited to the followingstructures, including (meth)acryloyl, vinyl, styrenic and ethynyl, thatare more fully described in reference to the preparation of thecompounds below.

Generally, the intermediate is reacted with an unsaturated compound ofthe formula:

whereinX⁶ is a functional group that is co-reactive with X² functional group ofthe intermediate, R⁴ is hydrogen, a C₁ to C₄ alkyl group, R⁶ is a singlebond or a divalent (hetero)hydrocarbyl linking group that joins theethylenically unsaturated group to reactive functional group X⁶, and xis 1 or 2.

More specifically, R⁶ is a single bond or a divalent linking group thatjoins an ethylenically unsaturated group to co-reactive functional groupX⁶ and preferably contains up to 34, preferably up to 18, morepreferably up to 10, carbon atoms and, optionally, oxygen and nitrogenatoms, optional catenary ester, amide, urea, urethane and carbonategroups. When R⁶ may further include linking groups selected from —O—.—S—, —NR⁴—, —SO₂—, —PO₂—, —CO—, —OCO—, —NR⁵—CO—, NR⁵—CO—O—, NR⁵—CO—NR⁴—,—R⁷— and combinations thereof, such as —CO—O—R⁷—, —CO—NR⁵—R⁷—, and—R⁷—CO—O—R⁷—, wherein each R⁵ is hydrogen, a C₁ to C₄ alkyl group, oraryl group, each R⁷ is an alkylene group having 1 to 6 carbon atoms, a5- or 6-membered cycloalkylene group having 5 to 10 carbon atoms, or adivalent aromatic group having 6 to 16 carbon atoms; and X⁶ is areactive functional group capable of reacting with a co-reactivefunctional group for the incorporation of a free-radically polymerizablefunctional “Z” group.

It will be understood that reaction between the X² functional groups ofthe intermediate and the X⁶ group of Formulas Va,b will form the R²—Y—moiety of Formula I, with the proviso that —R²—Y does not containperoxidic linkages, i.e. O—O, N—O, S—O, N—N, N—S bonds.

More particularly, the compound of Formula V may be of the formula:

Y¹—R³—O—CO—CR⁴═CH₂,  VIIa

where Y¹ is an electrophilic functional group reactive with nucleophilicX² groups, R³ is a (hetero)hydrocarbyl group, preferably alkylene, R⁴ isH or C₁-C₄ alkyl, or of the formula

Y²—R³—O—CO—CR⁴═CH₂,  VIIb

where Y² is an nucleophilic functional group reactive with electrophilicX² groups, R³ is (hetero)hydrocarbyl group, preferably alkylene, and R⁴is H or C₁-C₄ alkyl.

In reference to Formula V, particularly useful Z—X¹— groups includeH₂C═C(CH₃)C(O)—O—CH₂—CH(OH)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH₂—CH(O—(O)C(CH₃)═CH₂)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH(CH₂OPh)-CH₂—O—,H₂C═C(CH₃)C(O)—O—CH₂CH₂—N(H)—C(O)—O—CH(CH₂OPh)-CH₂—O—.,H₂C═C(CH₃)C(O)—O—CH₂—CH(O—(O)C—N(H)—CH₂CH₂—O—(O)C(CH₃)C═CH₂)—CH₂—O—,H₂C═C(H)C(O)—O—(CH₂)₄—O—CH₂—CH(OH)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH₂—CH(O—(O)C—N(H)—CH₂CH₂—O—(O)C(CH₃)C═CH₂)—CH₂—O—,CH₃—(CH₂)₇—CH(O—(O)C—N(H)—CH₂CH₂—O—(O)C(CH₃)C═CH₂)—CH₂—O—,H₂C═C(H)C(O)—O—(CH₂)₄—O—CH₂—CH(—O—(O)C(H)═CH₂)—CH₂—O— andH₂C═C(H)C(O)—O—CH₂—CH(OH)—CH₂—O—.H₂C═C(H)C(O)—O—(CH₂)₄—O—CH₂—CH(—O—(O)C(H)—CH₂)—CH₂—O—, andCH₃—(CH₂)₇—CH(O—(O)C—N(H)—CH₂CH₂—O—(O)C(CH₃)C═CH₂)—CH₂—O—.

As described supra, a portion of the X² groups intermediate may bereacted with a compound of the formula:

(R^(RI))_(d)—X³,  VI

where R^(RI) comprises high refractive index group, and X³ is a reactivefunctional group, reactive with the X² groups of the intermediate. Asdescribed for the Z group, the requisite high refractive index group maybe incorporated into the intermediate by means including addition,condensation, substitution and displacement reaction.

More particularly, the compound of Formula VI may be of the formula:

Y¹—(R³)_(q)—X⁴—R^(RI)*,  VIa

where Y¹ is an electrophilic functional group reactive with nucleophilicX² groups, R³ is a (hetero)hydrocarbyl group, preferably alkylene, q is0 or 1, X⁴ is selected from a covalent bond or a divalent linking groupincluding —O—, —O—CO—, —O—CO—NH—, —S—, —NH—, —NH—CO—, —NH—CO—NH,—NH—CO—O—, —O—CO—NHand R^(RI)* is a high refractive index group;or of the formula

Y²—(R³)_(q)—X⁴—R^(RI)*,  VIb

where Y² is an nucleophilic functional group reactive with electrophilicX² groups, R³ is (hetero)hydrocarbyl group, preferably alkylene, q is 0or 1, X⁴ is selected from a covalent bond or a divalent linking groupincluding —O—, —O—CO—, —O—CO—NH—, —S—, —NH—, —NH—CO—, —NH—CO—NH,—NH—CO—O—, —O—CO—NH and R^(RI)* is a high refractive index group.

Useful Y¹ and Y² groups of compounds of formula VIa,b include hydroxyl,amino, oxazolinyl, oxazolonyl, acetyl, acetonyl, carboxyl, isocyanato,epoxy, aziridinyl, acyl halide, halide and cyclic anhydride groups.Where the reactive functional group X² is an isocyanato functionalgroup, the co-reactive functional Y² group preferably comprises a aminoor hydroxyl group. Where the pendent reactive functional group X²comprises a hydroxyl group, the co-reactive functional group Y¹preferably comprises a carboxyl, ester, acyl halide, isocyanato, epoxy,anhydride, azlactonyl or oxazolinyl group. Where the pendent reactivefunctional group comprises a X² carboxyl group, the co-reactivefunctional Y² group preferably comprises a hydroxyl, amino, epoxy,isocyanate, or oxazolinyl group.

Useful high refractive functional groups include benzyl, 2-, 3-, and4-biphenyl, 1-, 2, 3-, 4-, and 9-fluorenyl,4-(1-methyl-1-phenethyl)phenoxyethyl; phenylthio; 1-, 2-, 3- and4-napthyl, 1- and 2-naphthylthio; 2,4,6-tribromophenoxy;2,4-dibromophenoxy; 2-bromophenoxy; 1-, and 2-naphthyloxy; 3-phenoxy-;2-, 3- and 4-phenylphenoxy; 2,4-dibromo-6-sec-butylphenyl;2,4-dibromo-6-isopropylphenyl; 2,4-dibromophenyl; pentabromobenzyl andpentabromophenyl.

In certain embodiments the functional groups Y¹ and Y² may be connectedto the high refractive index group R^(RI)* by a covalent bond (X⁴ is“-”) and subscript q is 0.

The intermediate can be provided with the requisite ethylenicallyunsaturated group and high refractive index group in any sequence, orsimultaneously, provided the additional fragmentation agent of Formula Iresults.

In some preferred embodiments, the intermediate of Formula IV a glycidylmethacrylate dimer, where the epoxy groups may be functionalized asfollows:

Alternatively, the intermediate of Formula IV is the dimer ofmethacrylic acid, which is first functionalized with glycidylmethacrylate (gma) to produce the methacrylate-functional intermediate,the hydroxyl of which is then further functionalized to provide the highrefractive index group.

The starting methacrylate dimers may be prepared by free radicaladdition of a (meth)acryloyl monomer in the presence of a free radicalinitiator and a cobalt (II) complex catalyst using the process of U.S.Pat. No. 4,547,323 (Carlson), incorporated herein by reference.Alternatively, the (meth)acryloyl may be prepared using a cobalt chelatecomplex using the processes of U.S. Pat. No. 4,886,861 (Janowicz) orU.S. Pat. No. 5,324,879 (Hawthorne), incorporated herein by reference.In either process, the reaction mixture can contain a complex mixture ofdimers, trimers, higher oligomers and polymers and the desired dimer canbe separated from the mixture by distillation and/or recrystallization.Distillation further separates any cobalt species from the desireddimer. The present disclosure further provides a polymerizablecomposition comprising the addition-fragmentation agent of Formula I,and at least one polymerizable monomer, such as (meth)acryloyl monomers,including acrylate esters, amides, and acids to produce (meth)acrylatehomo- and copolymers. Generally, the addition-fragmentation agent ofFormula I is used in amounts of 0.1 to 10 parts by weight, preferably0.1 to 5 parts by weight, based on 100 parts by weight of total monomer.

The (meth)acrylate ester monomer useful in preparing the (meth)acrylatepolymer is a monomeric (meth)acrylic ester of a non-tertiary alcohol,which alcohol contains from 1 to 14 carbon atoms and preferably anaverage of from 4 to 12 carbon atoms.

Examples of monomers suitable for use as the (meth)acrylate estermonomer include the esters of either acrylic acid or methacrylic acidwith non-tertiary alcohols such as ethanol, 1-propanol, 2-propanol,1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol,2-methyl-1-butanol, 3-methyl-1-butanol, 1-hexanol, 2-hexanol,2-methyl-1-pentanol, 3-methyl-1-pentanol, 2-ethyl-1-butanol,3,5,5-trimethyl-1-hexanol, 3-heptanol, 1-octanol, 2-octanol,isooctylalcohol, 2-ethyl-1-hexanol, 1-decanol, 2-propylheptanol,1-dodecanol, 1-tridecanol, 1-tetradecanol, citronellol,dihydrocitronellol, and the like. In some embodiments, the preferred(meth)acrylate ester monomer is the ester of (meth)acrylic acid withbutyl alcohol or isooctyl alcohol, or a combination thereof, althoughcombinations of two or more different (meth)acrylate ester monomer aresuitable. In some embodiments, the preferred (meth)acrylate estermonomer is the ester of (meth)acrylic acid with an alcohol derived froma renewable source, such as 2-octanol, citronellol, ordihydrocitronellol.

In some embodiments it is desirable for the (meth)acrylic acid estermonomer to include a high T_(g) monomer. The homopolymers of these highT_(g) monomers have a T_(g) of at least 25° C., and preferably at least50° C. Examples of suitable monomers useful in the present inventioninclude, but are not limited to, t-butyl acrylate, methyl methacrylate,ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate,isobutyl methacrylate, s-butyl methacrylate, t-butyl methacrylate,stearyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate,isobornyl acrylate, isobornyl methacrylate, benzyl methacrylate, 3,3,5trimethylcyclohexyl acrylate, cyclohexyl acrylate, N-octyl acrylamide,and propyl methacrylate or combinations.

The (meth)acrylate ester monomer is present in an amount of up to 100parts by weight, preferably 85 to 99.5 parts by weight based on 100parts total monomer content used to prepare the polymer, exclusive ofthe amount of multifunctional (meth)acrylates. Preferably (meth)acrylateester monomer is present in an amount of 90 to 95 parts by weight basedon 100 parts total monomer content. When high T_(g) monomers areincluded, the copolymer may include up to 50 parts by weight, preferablyup to 20 parts by weight of the (meth)acrylate ester monomer component.

The polymer may further comprise an acid functional monomer, where theacid functional group may be an acid per se, such as a carboxylic acid,or a portion may be a salt thereof, such as an alkali metal carboxylate.Useful acid functional monomers include, but are not limited to, thoseselected from ethylenically unsaturated carboxylic acids, ethylenicallyunsaturated sulfonic acids, ethylenically unsaturated phosphonic orphosphoric acids, and mixtures thereof. Examples of such compoundsinclude those selected from acrylic acid, methacrylic acid, itaconicacid, fumaric acid, crotonic acid, citraconic acid, maleic acid, oleicacid, β-carboxyethyl (meth)acrylate, 2-sulfoethyl methacrylate, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid,vinylphosphonic acid, and mixtures thereof.

Due to their availability, acid functional monomers of the acidfunctional copolymer are generally selected from ethylenicallyunsaturated carboxylic acids, i.e. (meth)acrylic acids. When evenstronger acids are desired, acidic monomers include the ethylenicallyunsaturated sulfonic acids and ethylenically unsaturated phosphonicacids. The acid functional monomer is generally used in amounts of 0.5to 15 parts by weight, preferably 1 to 15 parts by weight, mostpreferably 5 to 10 parts by weight, based on 100 parts by weight totalmonomer.

The polymer may further comprise a polar monomer. The polar monomersuseful in preparing the copolymer are both somewhat oil soluble andwater soluble, resulting in a distribution of the polar monomer betweenthe aqueous and oil phases in an emulsion polymerization. As used hereinthe term “polar monomers” are exclusive of acid functional monomers.

Representative examples of suitable polar monomers include but are notlimited to 2-hydroxyethyl (meth)acrylate; N-vinylpyrrolidone;N-vinylcaprolactam; acrylamide; mono- or di-N-alkyl substitutedacrylamide; t-butyl acrylamide; dimethylaminoethyl acrylamide; N-octylacrylamide; poly(alkoxyalkyl) (meth)acrylates including2-(2-ethoxyethoxy)ethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate,2-methoxyethoxyethyl (meth)acrylate, 2-methoxyethyl methacrylate,polyethylene glycol mono(meth)acrylates; alkyl vinyl ethers, includingvinyl methyl ether; and mixtures thereof. Preferred polar monomersinclude those selected from the group consisting of 2-hydroxyethyl(meth)acrylate and N-vinylpyrrolidinone. The polar monomer may bepresent in amounts of 0 to 10 parts by weight, preferably 0.5 to 5 partsby weight, based on 100 parts by weight total monomer.

The polymer may further comprise a vinyl monomer. When used, vinylmonomers useful in the (meth)acrylate polymer include vinyl esters(e.g., vinyl acetate and vinyl propionate), styrene, substituted styrene(e.g., α-methyl styrene), vinyl halide, and mixtures thereof. As usedherein vinyl monomers are exclusive of acid functional monomers,acrylate ester monomers and polar monomers. Such vinyl monomers aregenerally used at 0 to 5 parts by weight, preferably 1 to 5 parts byweight, based on 100 parts by weight total monomer.

A multifunctional (meth)acrylate may be incorporated into the blend ofpolymerizable monomers (in addition to the addition-fragmentationagent). Examples of useful multifunctional (meth)acrylates include, butare not limited to, di(meth)acrylates, tri(meth)acrylates, andtetra(meth)acrylates, such as 1,6-hexanediol di(meth)acrylate,poly(ethylene glycol) di(meth)acrylates, polybutadiene di(meth)acrylate,polyurethane di(meth)acrylates, and propoxylated glycerintri(meth)acrylate, and mixtures thereof. The amount and identity ofmultifunctional (meth)acrylate is tailored depending upon application ofthe adhesive composition, for example, adhesives, hardcoats or dentalresins. Typically, the multifunctional (meth)acrylate is present inamounts up to 100 parts based on the weight of remaining polymerizablecomposition. In some embodiments the multifunctional (meth)acrylate isused in amounts of 50 parts by weight or more, based on the weight ofremaining polymerizable composition. In some embodiments, thecrosslinker may be present in amounts from 0.01 to 5 parts, preferably0.05 to 1 parts, based on 100 parts total monomers of the adhesivecomposition for adhesive applications, and greater amounts for hardcoatsor dental resins, as described herein.

In such embodiments, the copolymer may comprise:

-   -   i. up to 100 parts by weight, preferably 85 to 99.5 parts by        weight of an (meth)acrylic acid ester;    -   ii. 0 to 15 parts by weight, preferably 0.5 to 15 parts by        weight of an acid functional ethylenically unsaturated monomer;    -   iii. 0 to 15 parts by weight of a non-acid functional,        ethylenically unsaturated polar monomer;    -   iv. 0 to 5 parts vinyl monomer;    -   v. 0 to 100 parts of a multifunctional (meth)acrylate, relative        to i-iv;    -   vi. 0 to 5 parts of a polymerizable photoinitiator.    -   based on 100 parts by weight total monomer and    -   0.1 to 10 parts of the addition-fragmentation agent, relative to        100 parts total monomer.

The composition may be polymerized with either a thermal initiator orphotoinitiator. Any conventional free radical initiator may be used togenerate the initial radical. Examples of suitable thermal initiatorsinclude peroxides such as benzoyl peroxide, dibenzoyl peroxide, dilaurylperoxide, cyclohexane peroxide, methyl ethyl ketone peroxide,hydroperoxides, e.g., tert-butyl hydroperoxide and cumene hydroperoxide,dicyclohexyl peroxydicarbonate, 2,2,-azo-bis(isobutyronitrile), andt-butyl perbenzoate. Examples of commercially available thermalinitiators include initiators available from DuPont Specialty Chemical(Wilmington, Del.) under the VAZO trade designation including VAZO™ 67(2,2′-azo-bis(2-methybutyronitrile)) VAZO™ 64(2,2′-azo-bis(isobutyronitrile)) and VAZO™ 52(2,2′-azo-bis(2,2-dimethyvaleronitrile)), and Lucidol™ 70 from ElfAtochem North America, Philadelphia, Pa.

Useful photoinitiators include benzoin ethers such as benzoin methylether and benzoin isopropyl ether; substituted acetophenones such as 2,2-dimethoxyacetophenone, available as Irgacure™ 651 photoinitiator (CibaSpecialty Chemicals), 2,2 dimethoxy-2-phenyl-1-phenylethanone, availableas Esacure™ KB-1 photoinitiator (Sartomer Co.; West Chester, Pa.), anddimethoxyhydroxyacetophenone; substituted α-ketols such as2-methyl-2-hydroxy propiophenone; aromatic sulfonyl chlorides such as2-naphthalene-sulfonyl chloride; and photoactive oximes such as1-phenyl-1,2-propanedione-2-(O-ethoxy-carbonyl)oxime. Particularlypreferred among these are the substituted acetophenones.

The initiator is used in an amount effective to facilitate free radicaladdition to the addition-fragmentation crosslinking agent and the amountwill vary depending upon, e.g., the type of initiator, and the molecularweight of the polymer and the degree of functionalization desired. Theinitiators can be used in amounts from about 0.001 part by weight toabout 5 parts by weight based on 100 parts total monomer.

The curable composition may also include other additives. Examples ofsuitable additives include tackifiers (e.g., rosin esters, terpenes,phenols, and aliphatic, aromatic, or mixtures of aliphatic and aromaticsynthetic hydrocarbon resins), surfactants, plasticizers (other thanphysical blowing agents), nucleating agents (e.g., talc, silica, orTiO₂), pigments, dyes, reinforcing agents, solid fillers, stabilizers(e.g., UV stabilizers), and combinations thereof. The additives may beadded in amounts sufficient to obtain the desired properties for thecured composition being produced. The desired properties are largelydictated by the intended application of the resultant polymeric article.

Adjuvants may optionally be added to the compositions such as colorants,abrasive granules, anti-oxidant stabilizers, thermal degradationstabilizers, light stabilizers, conductive particles, tackifiers, flowagents, bodying agents, flatting agents, inert fillers, binders, blowingagents, fungicides, bactericides, surfactants, plasticizers, rubbertougheners and other additives known to those skilled in the art. Theyalso can be substantially unreactive, such as fillers, both inorganicand organic. These adjuvants, if present, are added in an amounteffective for their intended purpose.

In some embodiments, a toughening agent may be used. The tougheningagents which are useful in the present invention are polymeric compoundshaving both a rubbery phase and a thermoplastic phase such as: graftpolymers having a polymerized, diene, rubbery core and a polyacrylate,polymethacrylate shell; graft polymers having a rubbery, polyacrylatecore with a polyacrylate or polymethacrylate shell; and elastomericparticles polymerized in situ in the epoxide from free radicalpolymerizable monomers and a copolymerizable polymeric stabilizer.

Examples of useful toughening agents of the first type include graftcopolymers having a polymerized, diene, rubbery backbone or core towhich is grafted a shell of an acrylic acid ester or methacrylic acidester, monovinyl aromatic hydrocarbon, or a mixture thereof, such asdisclosed in U.S. Pat. No. 3,496,250 (Czerwinski), incorporated hereinby reference. Preferable rubbery backbones comprise polymerizedbutadiene or a polymerized mixture of butadiene and styrene. Preferableshells comprising polymerized methacrylic acid esters are lower alkyl(C₁-C₄) substituted methacrylates. Preferable monovinyl aromatichydrocarbons are styrene, alphamethylstyrene, vinyltoluene, vinylxylene,ethylvinylbenzene, isopropylstyrene, chlorostyrene, dichlorostyrene, andethylchlorostyrene. It is important that the graft copolymer contain nofunctional groups that would poison the catalyst.

Examples of useful toughening agents of the second type are acrylatecore-shell graft copolymers wherein the core or backbone is apolyacrylate polymer having a glass transition temperature below about0° C., such as polybutyl acrylate or polyisooctyl acrylate to which isgrafted a polymethacrylate polymer (shell) having a glass transitionabove about 25° C., such as polymethylmethacrylate.

The third class of toughening agents useful in the invention compriseselastomeric particles that have a glass transition temperature (T_(g))below about 25° C. before mixing with the other components of thecomposition. These elastomeric particles are polymerized from freeradical polymerizable monomers and a copolymerizable polymericstabilizer that is soluble in the resins. The free radical polymerizablemonomers are ethylenically unsaturated monomers or diisocyanatescombined with coreactive difunctional hydrogen compounds such as diols,diamines, and alkanolamines.

Useful toughening agents include core/shell polymers such asmethacrylate-butadiene-styrene (MBS) copolymer wherein the core iscrosslinked styrene/butadiene rubber and the shell is polymethylacrylate(for example, ACRYLOID KM653 and KM680, available from Rohm and Haas,Philadelphia, Pa.), those having a core comprising polybutadiene and ashell comprising poly(methyl methacrylate) (for example, KANE ACE M511,M521, B11A, B22, B31, and M901 available from Kaneka Corporation,Houston, Tex. and CLEARSTRENGTH C223 available from ATOFINA,Philadelphia, Pa.), those having a polysiloxane core and a polyacrylateshell (for example, CLEARSTRENGTH S-2001 available from ATOFINA andGENIOPERL P22 available from Wacker-Chemie GmbH, Wacker Silicones,Munich, Germany), those having a polyacrylate core and a poly(methylmethacrylate) shell (for example, PARALOID EXL2330 available from Rohmand Haas and STAPHYLOID AC3355 and AC3395 available from Takeda ChemicalCompany, Osaka, Japan), those having an MBS core and a poly(methylmethacrylate) shell (for example, PARALOID EXL2691A, EXL2691, andEXL2655 available from Rohm and Haas) and the like and mixtures thereof.Preferred modifiers include the above-listed ACRYLOID and PARALOIDmodifiers and the like, and mixtures thereof.

The toughening agent is useful in an amount equal to about 1-35%,preferably about 3-25%, based on the weight of the curable composition.The toughening agents of the instant invention add strength to thecomposition after curing without reacting with the component of thecurable composition or interfering with curing.

In some embodiments, the partially cured composition may be disposedbetween two substrates (or adherends), and subsequently fully cured toeffect a structural or semistructual bond between the substrates.Therefore the present disclosure provides structural and semi-structuraladhesives. “Semi-structural adhesives” are those cured adhesives thathave an overlap shear strength of at least about 0.5 MPa, morepreferably at least about 1.0 MPa, and most preferably at least about1.5 MPa. Those cured adhesives having particularly high overlap shearstrength, however, are referred to as structural adhesives. “Structuraladhesives” are those cured adhesives that have an overlap shear strengthof at least about 3.5 MPa, more preferably at least about 5 MPa, andmost preferably at least about 7 MPa.

Fillers

In some embodiments the crosslinkable composition may include filler. Insome embodiments the total amount of filler is at most 50 wt. %,preferably at most 30 wt. %, and more preferably at most 10 wt. %filler. Fillers may be selected from one or more of a wide variety ofmaterials, as known in the art, and include organic and inorganicfiller. Inorganic filler particles include silica, submicron silica,zirconia, submicron zirconia, and non-vitreous microparticles of thetype described in U.S. Pat. No. 4,503,169 (Randklev).

Filler components include nanosized silica particles, nanosized metaloxide particles, and combinations thereof. Nanofillers are alsodescribed in U.S. Pat. No. 7,090,721 (Craig et al.), U.S. Pat. No.7,090,722 (Budd et al.), U.S. Pat. No. 7,156,911 (Kangas et al.), andU.S. Pat. No. 7,649,029 (Kolb et al.).

In some embodiments the filler may be surface modified. A variety ofconventional methods are available for modifying the surface ofnanoparticles including, e.g., adding a surface-modifying agent tonanoparticles (e.g., in the form of a powder or a colloidal dispersion)and allowing the surface-modifying agent to react with thenanoparticles. Other useful surface-modification processes are describedin, e.g., U.S. Pat. No. 2,801,185 (Iler), U.S. Pat. No. 4,522,958 (Daset al.) U.S. Pat. No. 6,586,483 (Kolb et al.), each incorporated hereinby reference.

Surface-modifying groups may be derived from surface-modifying agents.Schematically, surface-modifying agents can be represented by theformula X—Y, where the X group is capable of attaching to the surface ofthe particle (i.e., the silanol groups of a silica particle) and the Ygroup is a reactive or non-reactive functional group. A non-functionalgroup does not react with other components in the system (e.g. thesubstrate). Non-reactive functional groups can be selected to render theparticle relatively more polar, relatively less polar or relativelynon-polar. In some embodiments the non-reactive functional group “Y” isa hydrophilic group such as an acid group (including carboxylate,sulfonate and phosphonate groups), ammonium group or poly(oxyethylene)group, or hydroxyl group. In other embodiments, “Y” may be a reactivefunctional groups such as an ethylenically unsaturated polymerizablegroup, including vinyl, allyl, vinyloxy, allyloxy, and (meth)acryloyl,that may be free-radically polymerized with the polymerizable resin ormonomers.

Such optional surface-modifying agents may be used in amounts such that0 to 100%, generally 1 to 90% (if present) of the surface functionalgroups (Si—OH groups) of the silica nanoparticles are functionalized.The number of functional groups is experimentally determined wherequantities of nanoparticles are reacted with an excess of surfacemodifying agent so that all available reactive sites are functionalizedwith a surface modifying agent. Lower percentages of functionalizationmay then be calculated from the result. Generally, the amount of surfacemodifying agent is used in amount sufficient to provide up to twice theequal weight of surface modifying agent relative to the weight ofinorganic nanoparticles. When used, the weight ratio of surfacemodifying agent to inorganic nanoparticles is preferably 2:1 to 1:10. Ifsurface-modified silica nanoparticles are desired, it is preferred tomodify the nanoparticles prior to incorporation into the coatingcomposition.

In some embodiments the surface modified filler may be selected from theaddition-fragmentation agent modified filers as described in Applicant'scopending applications WO 2013/028397 and PCT/US2013/068207, eachincorporated herein by reference.

The present addition fragmentation agents are also useful in thepreparation of hardcoats. The term “hardcoat” or “hardcoat layer” meansa layer or coating that is located on the external surface of an object,where the layer or coating has been designed to at least protect theobject from abrasion. The present disclosure provides hardcoatcompositions comprising the addition-fragmentation agent of Formula Iand, a multi-functional (moth)acrylate monomer comprising three or more(meth)acrylate groups, and/or a multi-functional (meth)acrylate oligomerand optionally a (meth)acrylate-functional diluent.

Useful multifunctional (meth)acrylate monomers comprise three or more(meth)acrylate groups. Multifunctional (meth)acrylate monomers areuseful in the practice of the present invention because they addabrasion resistance to the hard coat layer. Preferred multifunctional(meth)acrylate monomers comprising three or more (meth)acrylate groupsinclude trimethylol propane tri(meth)acrylate (TMPTA), pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentrithritoltri(meth)acrylate (Sartomer 355), dipentaerythritol penta(meth)acrylate(Sartomer 399), dipentaerythritol hydroxy penta(meth)acrylate (DPHPA),glyceryl propoxy tri(meth)acrylate, trimethylopropane tri(meth)acrylate,and mixtures thereof. Another useful radiation-curable component of thepresent invention is the class of multifunctional (meth)acrylateoligomers, having two or more (meth)acrylate groups, and having anaverage molecular weight (Mw) in the range from about 400 to 2000.

Useful multi-functional (meth)acrylate oligomers include polyester(meth)acrylates, polyurethane (meth)acrylates, and (meth)acrylated epoxy(meth)acrylates. (Meth)acrylated epoxy (meth)acrylates andpolyester(meth)acrylates are most preferred because they tend to have arelatively low viscosity and therefore allow a more uniform layer to beapplied by the spin coating method. Specifically, preferredmultifunctional (meth)acrylate oligomers include those commerciallyavailable from UCB Radcure, Inc. of Smyrna, Ga. and sold under the tradename Ebecryl (Eb): Eb40 (tetrafunctional acrylated polyester oligomer),ENO (polyester tetrafunctional (meth)acrylate oligomer), Eb81(multifunctional (meth)acrylated polyester oligomer), Eb600 (bisphenol Aepoxy di(meth)acrylate), Eb605 (bisphenol A epoxy di(meth)acrylatediluted with 25% tripropylene glycol di(meth)acrylate), Eb639 (novolacpolyester oligomer), Eb2047 (trifunctional acrylated polyesteroligomer), Eb3500 (di-functional Bisphenol-A oligomer acrylate), Eb3604(multi-functional polyester oligomer acrylate), Eb6602 (trifunctionalaromatic urethane acrylate oligomer), Eb8301 (hexafunctional aliphaticurethane acrylate), EbW2 (difunctional aliphatic urethane acrylateoligomer), and mixtures thereof. Of these, the most preferred are, Eb600, Eb605, Eb80, and Eb81.

The (meth)acrylate-functional diluents, also referred to herein as“reactive diluents”, are relatively low molecular weight mono- ordi-functional, non-aromatic, (meth)acrylate monomers. These relativelylow molecular weight reactive diluents are advantageously of arelatively low viscosity, e.g., less than about 30 centipoise (cps) at25° C. Di-functional, non-aromatic (meth)acrylates are generallypreferred over mono-functional non-aromatic (meth)acrylates becausedi-functional non-aromatic (meth)acrylates allow for quicker cure time.Preferred reactive diluents include 1,6-hexanediol di(meth)acrylate(HDDA from UCB Radcure, Inc. of Smyrna, Ga.), tripropylene glycoldi(meth)acrylate, isobornyl (meth)acrylate (1130A, Radcure),2(2-ethoxyethoxy) ethyl (meth)acrylate (sold under the trade nameSartomer 256 from SARTOMER Company, Inc. of Exton, Pa.), n-vinylformamide (Sartomer 497), tetrahydrofurfuryl (meth)acrylate (Sartomer285), polyethylene glycol di(meth)acrylate (Sartomer 344), tripropyleneglycol di(meth)acrylate (Radcure), neopentyl glycol dialkoxydi(meth)acrylate, polyethyleneglycol di(meth)acrylate, and mixturesthereof.

The hardcoat composition may comprise:

0.1-10 wt. % of the addition fragmentation agent of Formula I;

20-80 wt. % of multifunctional (meth)acrylate monomers and/ormultifunctional (meth)acrylate oligomers,

0 to 25 wt. % range of (meth)acrylate diluent, (0-25 wt. %)

20 to 75 wt. % of silica. The weight ranges referring to the silica perse, whether or not functionalized.

In some embodiments the amount of silica, including the silica modifiedwith conventional surface modifying agents and unmodified silica is20-75 wt. %, preferably 50-70 wt. %.

Filler components include nanosized silica particles, nanosized metaloxide particles, and combinations thereof. Nanofillers are alsodescribed in U.S. Pat. No. 7,090,721 (Craig et al.), U.S. Pat. No.7,090,722 (Budd et al.), U.S. Pat. No. 7,156,911 (Kangas et al.), andU.S. Pat. No. 7,649,029 (Kolb et al.).

The present disclosure further provides curable dental compositionscomprising the addition-fragmentation agent of Formulas I or Ia.Although various curable dental compositions have been described,industry would find advantage in compositions having improved propertiessuch as reduced stress deflection and/or reduced shrinkage whilemaintaining sufficient mechanical properties and depth of cure.

As used herein, “dental composition” refers to a material, optionallycomprising filler, capable of adhering or being bonded to an oralsurface. A curable dental composition can be used to bond a dentalarticle to a tooth structure, form a coating (e.g., a sealant orvarnish) on a tooth surface, be used as a restorative that is placeddirectly into the mouth and cured in-situ, or alternatively be used tofabricate a prosthesis outside the mouth that is subsequently adheredwithin the mouth.

Curable dental compositions include, for example, adhesives (e.g.,dental and/or orthodontic adhesives), cements (e.g., resin-modifiedglass ionomer cements, and/or orthodontic cements), primers (e.g.,orthodontic primers), liners (applied to the base of a cavity to reducetooth sensitivity), coatings such as sealants (e.g., pit and fissure),and varnishes; and resin restoratives (also referred to as directcomposites) such as dental fillings, as well as crowns, bridges, andarticles for dental implants. Highly filled dental compositions are alsoused for mill blanks, from which a crown may be milled. A composite is ahighly filled paste designed to be suitable for filling substantialdefects in tooth structure. Dental cements are somewhat less filled andless viscous materials than composites, and typically act as a bondingagent for additional materials, such as inlays, onlays and the like, oract as the filling material itself if applied and cured in layers.Dental cements are also used for permanently bonding dental restorationssuch as a crown or bridge to a tooth surface or an implant abutment.

As used herein:

“dental article” refers to an article that can be adhered (e.g., bonded)to a tooth structure or dental implant. Dental articles include, forexample, crowns, bridges, veneers, inlays, onlays, fillings, orthodonticappliances and devices.

“orthodontic appliance” refers to any device intended to be bonded to atooth structure, including, but not limited to, orthodontic brackets,buccal tubes, lingual retainers, orthodontic bands, bite openers,buttons, and cleats. The appliance has a base for receiving adhesive andit can be a flange made of metal, plastic, ceramic, or combinationsthereof. Alternatively, the base can be a custom base formed from curedadhesive layer(s) (i.e. single or multi-layer adhesives).

“oral surface” refers to a soft or hard surface in the oral environment.Hard surfaces typically include tooth structure including, for example,natural and artificial tooth surfaces, bone, and the like.

“curable” is descriptive of a material or composition that can bepolymerized or crosslinked by a free-radical means such as byirradiating with actinic irradiation to induce polymerization and/orcrosslinking; “hardened” refers to a material or composition that hasbeen cured (e.g., polymerized or crosslinked).

“initiator” refers to something that initiates curing of a resin. Aninitiator may include, for example, a polymerization initiator system, aphotoinitiator system, a thermal initiator and/or a redox initiatorsystem.

“self-etching” composition refers to a composition that bonds to adental structure surface without pretreating the dental structuresurface with an etchant. Preferably, a self-etching composition can alsofunction as a self-primer wherein no separate etchant or primer areused.

a “self-adhesive” composition refers to a composition that is capable ofbonding to a dental structure surface without pretreating the dentalstructure surface with a primer or bonding agent.

Preferably, a self-adhesive composition is also a self-etchingcomposition wherein no separate etchant is used.

a “dental structure surface” refers to tooth structures (e.g., enamel,dentin, and cementum) and bone.

an “uncut” dental structure surface refers to a dental structure surfacethat has not been prepared by cutting, grinding, drilling, etc.

an “untreated” dental structure surface refers to a tooth or bonesurface that has not been treated with an etchant, primer, or bondingagent prior to application of a self-etching adhesive or a self-adhesivecomposition of the present invention.

an “unetched” dental structure surface refers to a tooth or bone surfacethat has not been treated with an etchant prior to application of aself-etching adhesive or a self-adhesive composition of the presentinvention.

The total amount of addition-fragmentation agent(s) in the polymerizableresin portion of the unfilled curable dental composition is typically nogreater than 15 wt. %. As the concentration of theaddition-fragmentation monomer increases, the stress deflection andWatts Shrinkage typically decrease. However, when the amount ofaddition-fragmentation agent exceeds an optimal amount, mechanicalproperties such as Diametral tensile strength and/or Barcol hardness, ordepth of cure may be insufficient.

The polymerizable resin portion of the curable dental compositiondescribed herein comprises at least 0.1 wt. %, of addition-fragmentationagent(s). Generally, the amount of addition-fragmentation agent is fromabout 0.5 to 10 wt. % of the polymerizable portion of the unfilleddental composition.

The filled curable dental composition described herein typicallycomprises at least 0.1 wt. %, of addition-fragmentation agent(s). Thetotal amount of addition-fragmentation agent(s) in the filled curabledental composition is typically no greater than 5 wt. %.

Materials with high polymerization stress upon curing generate strain inthe tooth structure. One clinical consequence of such stress can be adecrease in the longevity of the restoration. The stress present in thecomposite passes through the adhesive interface to the tooth structuregenerating cuspal deflection and cracks in the surrounding dentin andenamel which can lead to postoperative sensitivity as described in R. R.Cara et al, Particulate Science and Technology 28; 191-206 (2010).Preferred (e.g. filled) dental compositions (useful for restorationssuch as fillings and crowns) described herein typically exhibit a stressdeflection of no greater than 2.0, or 1.8, or 1.6, or 1.4, or 1.2 or 1.0or 0.8 or 0.6 microns.

The curable compositions described herein further comprise at least oneethylenically unsaturated resin monomer or oligomer in combination withthe addition-fragmentation agent. In some embodiments, such as primers,the ethylenically unsaturated monomer may be monofunctional, having asingle (e.g. terminal) ethylenically unsaturated group. In otherembodiments, such as dental restorations the ethylenically unsaturatedmonomer is multifunctional. The phrase “multifunctional ethylenicallyunsaturated” means that the monomers each comprise at least twoethylenically unsaturated (e.g. free radically) polymerizable groups,such as (meth)acrylate groups.

The amount of curable resin in the dental composition is a function ofthe desired end use (adhesives, cements, restoratives, etc.) and can beexpressed with respect to the (i.e. unfilled) polymerizable resinportion of the dental composition. For favored embodiments, wherein thecomposition further comprises filler, the concentration of monomer canalso be expressed with respect to the total (i.e. filled) composition.When the composition is free of filler, the polymerizable resin portionis the same as the total composition.

In favored embodiments, such ethylenically unsaturated groups of thecurable dental resin includes (meth)acryloyl such as (meth)acrylamideand (meth)acrylate. Other ethylenically unsaturated polymerizable groupsinclude vinyl and vinyl ethers. The ethylenically unsaturated terminalpolymerizable group(s) is preferably a (meth)acrylate group,particularly for compositions that are hardened by exposure to actinic(e.g. UV and visible) radiation. Further, methacrylate functionality istypically preferred over the acrylate functionality in curable dentalcompositions. The ethylenically unsaturated monomer may comprise variousethylenically unsaturated monomers, as known in the art, for use indental compositions.

In favored embodiments, the (e.g. dental) composition comprises one ormore dental resins having a low volume shrinkage monomer. Preferred(e.g. filled) curable dental compositions (useful for restorations suchas fillings and crowns) comprise one or more low volume shrinkage resinssuch that the composition exhibits a Watts Shrinkage of less than about2%, preferably no greater than 1.80%, more no greater than 1.60%. Infavored embodiments, the Watts Shrinkage is no greater than 1.50%, or nogreater than 1.40%, or no greater than 1.30%, and in some embodiments nogreater than 1.25%, or no greater than 1.20%, or no greater than 1.15%,or no greater than 1.10%.

Preferred low volume shrinkage monomers include isocyanurate resins,such as described in U.S.S.N. 2013/0012614 (Abuelyaman et al.);tricyclodecane resins, such as described in U.S.S.N 2011/041736 (Eckertet al.); polymerizable resins having at least one cyclic allylic sulfidemoiety such as described in U.S. Pat. No. 7,888,400 (Abuelyaman et al.);methylene dithiepane silane resins as described in U.S. Pat. No.6,794,520 (Moszner et al.); and di-, tri, and/ortetra-(meth)acryloyl-containing resins such as described in U.S.2010/021869 (Abuelyaman et al.); each of which are incorporated hereinby reference.

In favored embodiments, the majority of the (e.g. unfilled)polymerizable resin composition comprises one or more low volumeshrinkage monomers (“Low shrinkage monomers”). For example, at least50%, 60%, 70%, 80%, 90% or more of the (e.g. unfilled) polymerizableresin may comprise low volume shrinkage monomer(s).

In one embodiment, the dental composition comprises at least oneisocyanurate resin. The isocyanurate resin comprises a trivalentisocyanuric acid ring as an isocyanurate core structure and at least twoethylenically unsaturated (e.g. free radically) polymerizable groupsbonded to at least two of the nitrogen atoms of the isocyanurate corestructure via a (e.g. divalent) linking group. The linking group is theentire chain of atoms between the nitrogen atom of the isocyanurate corestructure and the terminal ethylenically unsaturated group. Theethylenically unsaturated (e.g. free radically) polymerizable groups aregenerally bonded to the core or backbone unit via a (e.g. divalent)linking group.

The trivalent isocyanurate core structure generally has the formula:

The divalent linking group comprises at least one nitrogen, oxygen orsulfur atom. Such nitrogen, oxygen or sulfur atom forms an urethane,ester, thioester, ether, or thioether linkage. Ether and especiallyester linkages can be beneficial over isocyanurate resin comprisingurethane linkages for providing improved properties such as reducedshrinkage, and/or increased mechanical properties, e.g., diametraltensile strength (DTS). Thus, in some embodiments, the divalent linkinggroups of the isocyanurate resin are free of urethane linkages. In somefavored embodiments, the divalent linking group comprises an esterlinkage such as an aliphatic or aromatic diester linkage.

The isocyanurate monomer typically has the general structure:

wherein R⁷ is a (hetero)hydrocarbyl group including straight chain,branched or cyclic alkylene, arylene, or alkarylene, and optionallyincluding a heteroatom (e.g. oxygen, nitrogen, or sulfur); R⁴ ishydrogen or C1-C4 alkyl; R⁸ is heterohydrocarbyl group includingalkylene, arylene, or alkarylene linking group comprising at least onemoiety selected from urethane, ester, thioester, ether, or thioether,and combinations of such moieties; and at least one of the R⁹ groups is

R⁷ is typically a straight chain, branched or cyclic alkylene,optionally including a heteroatom, having no greater than 12 carbonsatoms. In some favored embodiments, R⁷ has no greater than 8, 6, or 4carbon atoms. In some favored embodiments, R₇ comprises at least onehydroxyl moiety.

In some embodiments, R⁸ comprises an aliphatic or aromatic ester linkagesuch as a diester linkage.

In some embodiment, R⁸ further comprises one or more ether moieties.Hence, the linking group may comprise a combination of ester or diestermoieties and one or more ether moieties.

For embodiments, wherein the isocyanurate monomer is a di(meth)acrylatemonomer, R⁹ is hydrogen, alkyl, aryl, or alkaryl, optionally including aheteroatom.

The polymerizable resin portion of the curable unfilled dentalcomposition described herein may comprise at least 10 wt. %, 15 wt. %,20 wt. %, or 25 wt. %, multifunctional ethylenically unsaturatedisocyanurate resin(s). The isocyanurate resin may comprise a singlemonomer or a blend of two or more isocyanurate resins. The total amountof isocyanurate resin(s) in the unfilled polymerizable resin portion ofthe curable dental composition is typically no greater than 90 wt. %, 85wt. %, 80 wt. %, or 75 wt. %.

The filled curable dental composition described herein

typically comprises at least 5 wt. %, 6 wt. %, 7 wt. %, 8 wt. %, or 9wt. % of multifunctional ethylenically unsaturated isocyanurateresin(s). The total amount of isocyanurate resin(s) of the filledhardenable (i.e. polymerizable) dental composition is typically nogreater than 20 wt. %, or 19 wt. %, or 18 wt. %, or 17 wt. %, or 16 wt.%, or 15 wt. %.

In another embodiment, the dental composition comprises at least onetricyclodecane resin. The tricyclodecane resin may comprise a singlemonomer or a blend of two or more tricyclodecane resins. Theconcentration of multifunctional ethylenically unsaturatedtricyclodecane monomer in the (i.e. unfilled) polymerizable resinportion or filled hardenable (i.e. polymerizable) composition can be thesame as just described for the multifunctional ethylenically unsaturatedisocyanurate monomer.

Tricyclodecane monomers generally have the core structure (i.e. backboneunit (U):

The backbone unit (U) if the tricyclodecane resin typically comprisesone or two spacer unit(s) (S) bonded to the backbone unit (U) via anether linkage. At least one spacer unit (S) comprises a CH(R10)-OGchain, wherein each group G comprises a (meth)acrylate moiety and R10(comprises at least one group selected from hydrogen, alkyl, aryl,alkaryl and combinations thereof. In some embodiments, R10 is hydrogen,methyl, phenyl, phenoxymethyl, and combinations thereof. G may be bondedto the spacer unit(s) (S) via a urethane moiety.

In some embodiments, the spacer unit(s) (S) typically comprise

wherein m is 1 to 3; n is 1 to 3; and R¹⁰ is hydrogen, methyl, phenyl,phenoxymethyl.

In other embodiments, the spacer unit(s) (S) typically comprise

wherein M=aryl.

In some embodiments the composition comprises a multifunctionalethylenically unsaturated isocyanurate monomer and multifunctionalethylenically unsaturated tricyclodecane monomer at a weight ratioranging from about 1.5:1 to 1:1.5.

In some embodiments, the curable dental composition comprises apolymerizable resin having at least one cyclic allylic sulfide moietywith at least one (meth)acryloyl moiety.

The cyclic allylic sulfide moiety typically comprises at least one 7- or8-membered ring that has two heteroatoms in the ring, one of which issulfur. Most typically both of the heteroatoms are sulfur, which mayoptionally be present as part of an SO, SO₂, or S—S moiety. In otherembodiments, the ring may comprise a sulfur atom plus a second,different heteroatom in the ring, such as oxygen or nitrogen. Inaddition, the cyclic allylic moiety may comprise multiple ringstructures, i.e. may have two or more cyclic allylic sulfide moieties.The (meth)acryloyl moiety is preferably a (meth)acryloyloxy (i.e. a(meth)acrylate moiety) or a (meth)acryloylamino (i.e., a(meth)acrylamide moiety).

In one embodiment, the low shrinkage resin includes those represented bythe formulae:

In the above formulae, each A can be independently selected from S, O,N, C (e.g., C(R¹⁰)₂, where each R¹⁰ is independently a H or an organicgroup), SO, SO₂, N-alkyl, N-acyl, NH, N-aryl, carboxyl or carbonylgroup, provided that at least one X is S or a group comprising S.Preferably, each A is sulfur.

B is either alkylene (e.g., methylene, ethylene, etc.) optionallyincluding a heteroatom, carbonyl, or acyl; or is absent, therebyindicating the size of the ring, typically 7- to 10-membered rings,however larger rings are also contemplated. Preferably, the ring iseither a 7- or 8-membered ring with B thus being either absent ormethylene, respectively. In some embodiments, B is either absent or is aC1 to C3 alkylene, optionally including a heteroatom, carbonyl, acyl, orcombinations thereof.

X¹ is independently —O— or —NR⁴—, where R⁴ is H or C₁-C₄ alkyl.

The R¹¹ group represents a linker selected from alkylene (typicallyhaving more than one carbon atom, i.e. excluding methylene), alkyleneoptionally including a heteroatom (e.g., O, N, S, S—S, SO, SO₂),arylene, cycloaliphatic, carbonyl, siloxane, amido (—CO—NH—), acyl(—CO—O—), urethane (—O—CO—NH—), and urea (—NH—CO—NH—) groups, andcombinations thereof. In certain embodiments, R′ comprises an alkylenegroup, typically a methylene or longer group, that may be eitherstraight chain or branched, and which can be either unsubstituted, orsubstituted with aryl, cycloalkyl, halogen, nitrile, alkoxy, alkylamino,dialkylamino, akylthio, carbonyl, acyl, acyloxy, amido, urethane group,urea group, a cyclic allylic sulfide moiety, or combinations thereof.

R⁴ is H or C₁-C₄ alkyl, and “a” and “b” are independently 1 to 3.

Optionally the cyclic allylic sulfide moiety can further be substitutedon the ring with one or more groups selected from straight or branchedchain alkyl, aryl, cycloalkyl, halogen, nitrile, alkoxy, alkylamino,dialkylamino, akylthio, carbonyl, acyl, acyloxy, amido, urethane group,and urea group. Preferably the selected substituents do not interferewith the hardening reaction. Preferred are cyclic allylic sulfidestructures that comprise unsubstituted methylene members.

A typical low shrinkage monomer can comprise an 8-membered cyclicallylic sulfide moiety with two sulfur atoms in the ring and with thelinker attached directly to the 3-position of the ring with an acylgroup (i.e., Ring-OC(O)—). Typically the weight average molecular weight(MW) of the hybrid monomer ranges from about 400 to about 900 and insome embodiments is at least 250, more typically at least 500, and mosttypically at least 800.

The inclusion of a polymerizable compound having at least one cyclicallylic sulfide moiety can result in a synergistic combination of lowvolume shrinkage in combination with high diametral tensile strength.

In another embodiment, the dental composition comprises a low shrinkageresin that includes at least one di-, tri-, and/or tetra(meth)acryloyl-containing resins having the general formula:

wherein: each X¹ is independently —O— or —NR⁴—, where R⁴ is H or C₁-C₄alkyl;D and E each independently represent an organic group, and R¹²represents —C(O)C(CH₃)═CH₂, and/or p=0 and R¹² represents H,—C(O)CH═CH₂, or —C(O)C(CH₃)═CH₂, with the proviso that at least one R¹²is a (meth)acrylate; each m is 1 to 5; p and q are independently 0 or 1.Although, this material is a derivative of bisphenol A, when other lowvolume shrinkage monomer are employed, such as the isocyanurate and/ortricyclodecane monomer, the dental composition is free of (meth)acrylatemonomers derived from bisphenol A. Such resins are described in WO2008/082881 (Abuelyaman et al.)

In another embodiment, the low shrinkage dental resin may be selectedfrom methylene dithiepane silane resins described in U.S. Pat. No.6,794,520 (Moszner et al.), incorporated herein by reference. Suchresins have the general formula

in which R¹⁴ is a saturated or unsaturated aliphatic or alicyclichydrocarbon radical with 1 to 10 carbon atoms, which can be interruptedby one or more oxygen and/or sulfur atoms and can contain one or moreester, carbonyl, amide and/or urethane groups, or is an aromatic orheteroaromatic hydrocarbon radical with 6 to 18 carbon atoms, thehydrocarbon radicals being able to be substituted or unsubstituted; R¹⁵has one of the meanings given for R¹⁴ or is absent; R¹⁶ has one of themeanings given for R¹⁴ or is absent; R¹⁷ is equal to —(CHR¹⁹)_(n)—,—W—CO—NH—(CHR¹⁹)_(n)—, —Y—CO—NH—R¹⁸—, —(CHR¹⁹)_(n), —SR¹⁸—, —CO—O—R¹⁸—or is absent, with n being equal to 1 to 4, R¹⁹ is hydrogen, C₁ to C₁₀alkyl or C₆ to C₁₀ aryl, R¹⁸ has one of the meanings given for R¹⁴ and Wstands for an O or S atom or is absent; with R¹⁸ and R¹⁹ being able tobe substituted or unsubstituted; R²⁰ is a hydrolyzable group; d, e, fand x each independently of each other being 1, 2 or 3; and the sum ofd+x=2 to 4.

The multifunctional low shrink resins are (e.g. highly) viscous liquidsat about 25° C., yet are flowable. The viscosity as can be measured witha Haake RotoVisco RV1 device, as described in EP Application No.10168240.9, filed Jul. 2, 2010 is typically at least 300, or 400, or 500Pa*s and no greater than 10,000 Pascal-seconds (Pa*s). In someembodiments, the viscosity is no greater than 5000 or 2500 Pa*s.

The ethylenically unsaturated resins of the dental composition aretypically stable liquids at about 25° C. meaning that the resins do notsubstantially polymerize, crystallize, or otherwise solidify when storedat room temperature (about 25° C.) for a typical shelf life of at least30, 60, or 90 days. The viscosity of the resins typically does notchange (e.g. increase) by more than 10% of the initial viscosity.

Particularly for dental restoration compositions, the ethylenicallyunsaturated resins generally have a refractive index of at least 1.50.In some embodiments, the refractive index is at least 1.51, 1.52, 1.53,or greater. The inclusion of sulfur atoms and/or the present of one ormore aromatic moieties can raise the refractive index (relative to thesame molecular weight resin lacking such substituents).

In some embodiments, the (unfilled) polymerizable resin may comprisesolely one or more low shrink resins in combination with the additionfragmentation agent(s). In other embodiments, the (unfilled)polymerizable resin comprises a small concentration of other monomer(s).By “other” is it meant an ethylenically unsaturated monomer such as a(meth)acrylate monomer that is not a low volume shrinkage monomer.

The concentration of such other monomer(s) is typically no greater than20 wt. %, 19 wt. %, 18 wt. %, 17 wt. %, 16 wt. %, or 15 wt. % of the(unfilled) polymerizable resin portion. The concentration of such othermonomers is typically no greater than 5 wt. %, 4 wt. %, 3 wt. %, or 2wt. % of the filled polymerizable dental composition.

In some embodiments, the “other monomers” of the dental compositioncomprise a low viscosity reactive (i.e. polymerizable) diluent. Reactivediluents typically have a viscosity of no greater than 300 Pa*s andpreferably no greater than 100 Pa*s, or 50 Pa*s, or 10 Pa*s. In someembodiments, the reactive diluent has a viscosity no greater than 1 or0.5 Pa*s. Reactive diluents are typically relatively low in molecularweight, having a molecular weight less than 600 g/mole, or 550 g/mol, or500 g/mole. Reactive diluents typically comprise one or twoethylenically unsaturated groups such as in the case ofmono(meth)acrylate or di(meth)acrylate monomers.

In some embodiments, the reactive diluent is an isocyanurate ortricyclodecane monomer. Tricyclodecane reactive diluent may have thesame generally structure as previously described. In favoredembodiments, the tricyclodecane reactive diluent

comprises one or two spacer unit(s) (S) being connected to the backboneunit (U) via an ether linkage; such as described in U.S. 2011/041736(Eckert et al.); incorporated herein by reference.

Although the inclusion of an addition fragmentation agent in a lowvolume shrinkage composition typically provides the lowest stress and/orlowest shrinkage, the addition fragmentation agents described herein canalso reduce the stress of dental composition comprising conventionalhardenable (meth)acrylate monomers, such as ethoxylated bisphenol Adimethacrylate (BisEMA6), 2-hydroxyethyl methacrylate (HEMA), bisphenolA diglycidyl dimethacrylate (bisGMA), urethane dimethacrylate (UDMA),triethlyene glycol dimethacrylate (TEGDMA), glycerol dimethacrylate(GDMA), ethyleneglycol dimethacrylate, neopentylglycol dimethacrylate(NPGDMA), and polyethyleneglycol dimethacrylate (PEGDMA).

The curable component of the curable dental composition can include awide variety of “other” ethylenically unsaturated compounds (with orwithout acid functionality), epoxy-functional (meth)acrylate resins,vinyl ethers, and the like.

The (e.g., photopolymerizable) dental compositions may include freeradically polymerizable monomers, agents, and polymers having one ormore ethylenically unsaturated groups. Suitable compounds contain atleast one ethylenically unsaturated bond and are capable of undergoingaddition polymerization. Examples of useful ethylenically unsaturatedcompounds include acrylic acid esters, methacrylic acid esters,hydroxy-functional acrylic acid esters, hydroxy-functional methacrylicacid esters, and combinations thereof.

Such free radically polymerizable compounds include mono-, di- orpoly-(meth)acrylates (i.e., acrylates and methacrylates) such as, methyl(meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-hexyl(meth)acrylate, stearyl (meth)acrylate, allyl (meth)acrylate, glyceroltri(meth)acrylate, ethyleneglycol di(meth)acrylate, diethyleneglycoldi(meth)acrylate, triethyleneglycol di(meth)acrylate, 1,3-propanedioldi(meth)acrylate, trimethylolpropane tri(meth)acrylate,1,2,4-butanetriol tri(meth)acrylate, 1,4-cyclohexanedioldi(meth)acrylate, pentaerythritol tetra(meth)acrylate, sorbitolhex(meth)acrylate, tetrahydrofurfuryl (meth)acrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,ethoxylated bisphenolA di(meth)acrylate, andtrishydroxyethyl-isocyanurate tri(meth)acrylate; (meth)acrylamides(i.e., acrylamides and methacrylamides) such as (meth)acrylamide,methylene bis-(meth)acrylamide, and diacetone (meth)acrylamide; urethane(meth)acrylates; the bis-(meth)acrylates of polyethylene glycols(preferably of molecular weight 200-500); and vinyl compounds such asstyrene, diallyl phthalate, divinyl succinate, divinyl adipate anddivinyl phthalate. Other suitable free radically polymerizable compoundsinclude siloxane-functional (meth)acrylates. Mixtures of two or morefree radically polymerizable compounds can be used if desired.

The curable dental composition may also contain a monomer havinghydroxyl groups and ethylenically unsaturated groups as an example of an“other monomer”. Examples of such materials include hydroxyalkyl(meth)acrylates, such as 2-hydroxyethyl (meth)acrylate and2-hydroxypropyl (meth)acrylate; glycerol mono- or di-(meth)acrylate;trimethylolpropane mono- or di-(meth)acrylate; pentaerythritol mono-,di-, and tri-(meth)acrylate; sorbitol mono-, di-, tri-, tetra-, orpenta-(meth)acrylate; and2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bisGMA).Suitable ethylenically unsaturated compounds are available from a widevariety of commercial sources, such as Sigma-Aldrich, St. Louis.

The curable dental compositions can include at least 1 wt. %, at least 3wt. %, or at least 5 wt. % ethylenically unsaturated compounds withhydroxyl functionality, based on the total weight of the unfilledcomposition. The compositions can include at most 80 wt. %, at most 70wt. %, or at most 60 wt. % ethylenically unsaturated compounds withhydroxyl functionality.

The dental compositions described herein may include one or more curablecomponents in the form of ethylenically unsaturated compounds with acidfunctionality as an example of an “other” monomer. When present, thepolymerizable component optionally comprises an ethylenicallyunsaturated compound with acid functionality. Preferably, the acidfunctionality includes an oxyacid (i.e., an oxygen-containing acid) ofcarbon, sulfur, phosphorous, or boron. Such acid-functional “other”monomers contribute to the self-adhesion or self-etching of the dentalcompositions as described in U.S. 2005/017966 (Falsafi et al.),incorporated herein by reference.

As used herein, ethylenically unsaturated compounds with acidfunctionality is meant to include monomers, oligomers, and polymershaving ethylenic unsaturation and acid and/or acid-precursorfunctionality. Acid-precursor functionalities include, for example,anhydrides, acid halides, and pyrophosphates. The acid functionality caninclude carboxylic acid functionality, phosphoric acid functionality,phosphonic acid functionality, sulfonic acid functionality, orcombinations thereof.

Ethylenically unsaturated compounds with acid functionality include, forexample, α,β-unsaturated acidic compounds such as glycerol phosphatemono(meth)acrylates, glycerol phosphate di(meth)acrylates, hydroxyethyl(meth)acrylate (e.g., HEMA) phosphates, bis((meth)acryloxyethyl)phosphate, bis((meth)acryloxypropyl) phosphate,bis((meth)acryloxy)propyloxy phosphate, (meth)acryloxyhexyl phosphate,bis((meth)acryloxyhexyl) phosphate, (meth)acryloxyoctyl phosphate,bis((meth)acryloxyoctyl) phosphate, (meth)acryloxydecyl phosphate,bis((meth)acryloxydecyl) phosphate, caprolactone methacrylate phosphate,citric acid di- or tri-methacrylates, poly(meth)acrylated oligomaleicacid, poly(meth)acrylated polymaleic acid, poly(meth)acrylatedpoly(meth)acrylic acid, poly(meth)acrylated polycarboxyl-polyphosphonicacid, poly(meth)acrylated polychlorophosphoric acid, poly(meth)acrylatedpolysulfonate, poly(meth)acrylated polyboric acid, and the like, may beused as components. Also monomers, oligomers, and polymers ofunsaturated carbonic acids such as (meth)acrylic acids, itaconic acid,aromatic (meth)acrylated acids (e.g., methacrylated trimellitic acids),and anhydrides thereof can be used.

The dental compositions can include an ethylenically unsaturatedcompound with acid functionality having at least one P—OH moiety. Suchcompositions are self-adhesive and are nonaqueous. For example, suchcompositions can include: a first compound including at least one(meth)acryloxy group and at least one —O—P(O)(OH)_(x) group, wherein x=1or 2, and wherein the at least one —O—P(O)(OH)_(x) group and the atleast one (meth)acryloxy group are linked together by a C₁-C₄hydrocarbon group; a second compound including at least one(meth)acryloxy group and at least one —O—P(O)(OH)_(x) group, wherein x=1or 2, and wherein the at least one —O—P(O)(OH)_(x) group and the atleast one (meth)acryloxy group are linked together by a C₅-C₁₂hydrocarbon group; an ethylenically unsaturated compound without acidfunctionality; an initiator system; and a filler.

The curable dental compositions can include at least 1 wt. %, at least 3wt. %, or at least 5 wt. % ethylenically unsaturated compounds with acidfunctionality, based on the total weight of the unfilled composition.The compositions can include at most 80 wt. %, at most 70 wt. %, or atmost 60 wt. % ethylenically unsaturated compounds with acidfunctionality.

The curable dental compositions may include resin-modified glass ionomercements such as those described in U.S. Pat. No. 5,130,347 (Mitra), U.S.Pat. No. 5,154,762 (Mitra), U.S. Pat. No. 5,925,715 (Mitra et al.) andU.S. Pat. No. 5,962,550 (Akahane). Such compositions can bepowder-liquid, paste-liquid or paste-paste systems. Alternatively,copolymer formulations such as those described in U.S. Pat. No.6,126,922 (Rozzi) are included in the scope of the invention.

An initiator is typically added to the mixture of polymerizableingredients (i.e. curable resins and the addition-fragmentation agent ofFormula I). The initiator is sufficiently miscible with the resin systemto permit ready dissolution in (and discourage separation from) thepolymerizable composition. Typically, the initiator is present in thecomposition in effective amounts, such as from about 0.1 weight percentto about 5.0 weight percent, based on the total weight of thecomposition.

The addition-fragmentation agent is generally free-radically cleavable.Although photopolymerization is one mechanism for generating freeradicals, other curing mechanisms also generate free radicals. Thus, theaddition-fragmentation agent does not require irradiation with actinicradiation (e.g. photocuring) in order to provide the reduction in stressduring curing.

In some embodiments, the mixture of resins is photopolymerizable and thecomposition contains a photoinitiator (i.e., a photoinitiator system)that upon irradiation with actinic radiation initiates thepolymerization (or hardening) of the composition. Suchphotopolymerizable compositions can be free radically polymerizable. Thephotoinitiator typically has a functional wavelength range from about250 nm to about 800 nm.

Suitable photoinitiators (i.e., photoinitiator systems that include oneor more compounds) for polymerizing free radically photopolymerizablecompositions include binary and tertiary systems. Typical tertiaryphotoinitiators include an iodonium salt, a photosensitizer, and anelectron donor compound as described in U.S. Pat. No. 5,545,676(Palazzotto et al.). Iodonium salts include diaryl iodonium salts, e.g.,diphenyliodonium chloride, diphenyliodonium hexafluorophosphate, anddiphenyliodonium tetrafluoroboarate. Some preferred photosensitizers mayinclude monoketones and diketones (e.g. alpha diketones) that absorbsome light within a range of about 300 nm to about 800 nm (preferably,about 400 nm to about 500 nm) such as camphorquinone,1-phenyl-1,2-propanedione, benzil, furil,3,3,6,6-tetramethylcyclohexanedione, phenanthraquinone and other cyclicalpha diketones. Of these camphorquinone is typically preferred.Preferred electron donor compounds include substituted amines, e.g.,ethyl 4-(N,N-dimethylamino)benzoate.

Other suitable photoinitiators for polymerizing free radicallyphotopolymerizable compositions include the class of phosphine oxidesthat typically have a functional wavelength range of about 380 nm toabout 1200 nm. Preferred phosphine oxide free radical initiators with afunctional wavelength range of about 380 nm to about 450 nm are acyl andbisacyl phosphine oxides.

Commercially available phosphine oxide photoinitiators capable offree-radical initiation when irradiated at wavelength ranges of greaterthan about 380 nm to about 450 nm includebis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide (IRGACURE 819, CibaSpecialty Chemicals, Tarrytown, N.Y.),bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl) phosphine oxide (CGI403, Ciba Specialty Chemicals), a 25:75 mixture, by weight, ofbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropan-1-one (IRGACURE 1700, Ciba SpecialtyChemicals), a 1:1 mixture, by weight, ofbis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropane-1-one (DAROCUR 4265, Ciba SpecialtyChemicals), and ethyl 2,4,6-trimethylbenzylphenyl phosphinate (LUCIRINLR8893X, BASF Corp., Charlotte, N.C.).

For this embodiment, suitable photoinitiators include those availableunder the trade designations IRGACURE and DAROCUR from Ciba SpecialityChemical Corp., Tarrytown, N.Y. and include 1-hydroxy cyclohexyl phenylketone (IRGACURE 184), 2,2-dimethoxy-1,2-diphenylethan-1-one (IRGACURE651), bis(2,4,6-trimethylbenzoyl)phenylphosphineoxide (IRGACURE 819),1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propane-1-one(IRGACURE 2959), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone(IRGACURE 369),2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (IRGACURE907), and 2-hydroxy-2-methyl-1-phenyl propan-1-one (DAROCUR 1173).

The photoinitiator may also be a polymerizable photoinitiator having afree-radically polymerizable groups and a photoinitiator group. Suchpolymerizable photoinitiators include 4-benzoylphenyl acrylate,2-(4-benzoylphenoxy)ethyl acrylate and2-[4-(2-hydroxy-2-methylpropanoyl)phenoxy]ethyl-N-acryloyl-2-methylalinate,and are described in U.S. Pat. No. 7,838,110 (Zhu et al.), U.S. Pat. No.5,506,279 (Babu et al.), incorporated herein by reference, and alsoTemel et al. “Photopolymerization and photophysical properties of aminelinked benzophenone photoinitiators for free radical polymerization”,Journal of Photochemistry and Photobiology A, Chemistry 219 (2011), pp.26-31.

The initiator is used in an amount effective to facilitate free radicaladdition to the addition-fragmentation crosslinking agent and the amountwill vary depending upon, e.g., the type of initiator and the molecularweight of the polymer and the degree of functionalization desired. Theinitiators can be used in amounts from about 0.001 part by weight toabout 5 parts by weight based on 100 parts total monomer.

The photopolymerizable compositions are typically prepared by admixingthe various components of the compositions. For embodiments wherein thephotopolymerizable compositions are not cured in the presence of air,the photoinitiator is combined under “safe light” conditions (i.e.,conditions that do not cause premature hardening of the composition).Suitable inert solvents may be employed if desired when preparing themixture.

Curing is affected by exposing the composition to a radiation source,preferably a visible light source. It is convenient to employ lightsources that emit actinic radiation light between 250 nm and 800 nm(particularly blue light of a wavelength of 380-520 nm) such as quartzhalogen lamps, tungsten-halogen lamps, mercury arcs, carbon arcs, low-,medium-, and high-pressure mercury lamps, plasma arcs, light emittingdiodes, and lasers. In general, useful light sources have intensities inthe range of 500-1500 mW/cm². A variety of conventional lights forhardening such compositions can be used.

The exposure may be accomplished in several ways. For example, thepolymerizable composition may be continuously exposed to radiationthroughout the entire hardening process (e.g., about 2 seconds to about60 seconds). It is also possible to expose the composition to a singledose of radiation, and then remove the radiation source, therebyallowing polymerization to occur. In some cases materials can besubjected to light sources that ramp from low intensity to highintensity. Where dual exposures are employed, the intensity of eachdosage may be the same or different. Similarly, the total energy of eachexposure may be the same or different.

The dental compositions comprising the multifunctional ethylenicallyunsaturated monomers may be chemically curable, i.e., the compositionscontain a chemical initiator (i.e., initiator system) that canpolymerize, cure, or otherwise harden the composition without dependenceon irradiation with actinic radiation. Such chemically curable (e.g.,polymerizable or curable) composition are sometimes referred to as“self-cure” compositions and may include redox cure systems, thermallycuring systems and combinations thereof. Further, the polymerizablecomposition may comprise a combination of different initiators, at leastone of which is suitable for initiating free radical polymerization.

The chemically hardenable compositions may include redox cure systemsthat include a polymerizable component (e.g., an ethylenicallyunsaturated polymerizable component) and redox agents that include anoxidizing agent and a reducing agent.

The reducing and oxidizing agents react with or otherwise cooperate withone another to produce free-radicals capable of initiatingpolymerization of the resin system (e.g., the ethylenically unsaturatedcomponent). This type of cure is a dark reaction, that is, it is notdependent on the presence of light and can proceed in the absence oflight. The reducing and oxidizing agents are preferably sufficientlyshelf-stable and free of undesirable colorization to permit theirstorage and use under typical conditions.

Useful reducing agents include ascorbic acid, ascorbic acid derivatives,and metal complexed ascorbic acid compounds as described in U.S. Pat.No. 5,501,727 (Wang et al.); amines, especially tertiary amines, such as4-tert-butyl dimethylaniline; aromatic sulfinic salts, such asp-toluenesulfinic salts and benzenesulfinic salts; thioureas, such as1-ethyl-2-thiourea, tetraethyl thiourea, tetramethyl thiourea,1,1-dibutyl thiourea, and 1,3-dibutyl thiourea; and mixtures thereof.Other secondary reducing agents may include cobalt (II) chloride,ferrous chloride, ferrous sulfate, hydrazine, hydroxylamine (dependingon the choice of oxidizing agent), salts of a dithionite or sulfiteanion, and mixtures thereof. Preferably, the reducing agent is an amine.

Suitable oxidizing agents will also be familiar to those skilled in theart, and include but are not limited to persulfuric acid and saltsthereof, such as sodium, potassium, ammonium, cesium, and alkyl ammoniumsalts. Additional oxidizing agents include peroxides such as benzoylperoxides, hydroperoxides such as cumyl hydroperoxide, t-butylhydroperoxide, and amyl hydroperoxide, as well as salts of transitionmetals such as cobalt (III) chloride and ferric chloride, cerium (IV)sulfate, perboric acid and salts thereof, permanganic acid and saltsthereof, perphosphoric acid and salts thereof, and mixtures thereof.

It may be desirable to use more than one oxidizing agent or more thanone reducing agent. Small quantities of transition metal compounds mayalso be added to accelerate the rate of redox cure. The reducing oroxidizing agents can be microencapsulated as described in U.S. Pat. No.5,154,762 (Mitra et al.). This will generally enhance shelf stability ofthe polymerizable composition, and if necessary permit packaging thereducing and oxidizing agents together. For example, through appropriateselection of an encapsulant, the oxidizing and reducing agents can becombined with an acid-functional component and optional filler and keptin a storage-stable state.

Curable dental compositions can also be cured with a thermally or heatactivated free radical initiator. Typical thermal initiators includeperoxides such as benzoyl peroxide and azo compounds such asazobisisobutyronitrile, as well as dicumyl peroxide, which is favoredfor mill blanks.

In favored embodiments, such as when the dental composition is employedas a dental restorative (e.g. dental filling or crown) or an orthodonticcement, the dental composition typically comprises appreciable amountsof (e.g. nanoparticle) filler. The amount of such fillers is a functionof the end use as further described herein. Such compositions preferablyinclude at least 40 wt. %, more preferably at least 45 wt. %, and mostpreferably at least 50 wt. % filler, based on the total weight of thecomposition. In some embodiments the total amount of filler is at most90 wt. %, preferably at most 80 wt. %, and more preferably at most 75wt. % filler.

The (e.g. filled) dental composite materials typically exhibit adiametral tensile strength (DTS) of at least about 70, 75, or 80 MPaand/or a Barcol Hardness of at least about 60, or 65, or 70. The ISO4049 depth of cure ranges from about 4 to about 5 mm and is comparableto commercially available (e.g. filled) dental compositions suitable forrestorations.

Dental compositions suitable for use as dental adhesives can optionallyalso include filler in an amount of at least 1 wt. %, 2 wt. %, 3 wt. %,4 wt. %, or 5 wt. % based on the total weight of the composition. Forsuch embodiments, the total concentration of filler is at most 40 wt. %,preferably at most 20 wt. %, and more preferably at most 15 wt. %filler, based on the total weight of the composition.

Fillers may be selected from one or more of a wide variety of materialssuitable for incorporation in compositions used for dental applications,such as fillers currently used in dental restorative compositions, andthe like.

The filler can be an inorganic material. It can also be a crosslinkedorganic material that is insoluble in the polymerizable resin, and isoptionally filled with inorganic filler. The filler is generallynon-toxic and suitable for use in the mouth. The filler can beradiopaque, radiolucent, or nonradiopaque. Fillers as used in dentalapplications are typically ceramic in nature.

Suitable inorganic filler particles include quartz (i.e., silica),submicron silica, zirconia, submicron zirconia, and non-vitreousmicroparticles of the type described in U.S. Pat. No. 4,503,169(Randklev).

The filler can also be an acid-reactive filler. Suitable acid-reactivefillers include metal oxides, glasses, and metal salts. Typical metaloxides include barium oxide, calcium oxide, magnesium oxide, and zincoxide. Typical glasses include borate glasses, phosphate glasses, andfluoroaluminosilicate (“FAS”) glasses. The FAS glass typically containssufficient elutable cations so that a hardened dental composition willform when the glass is mixed with the components of the hardenablecomposition. The glass also typically contains sufficient elutablefluoride ions so that the hardened composition will have cariostaticproperties. The glass can be made from a melt containing fluoride,alumina, and other glass-forming ingredients using techniques familiarto those skilled in the FAS glassmaking art. The FAS glass typically isin the form of particles that are sufficiently finely divided so thatthey can conveniently be mixed with the other cement components and willperform well when the resulting mixture is used in the mouth.

Generally, the average particle size (typically, diameter) for the FASglass is no greater than 12 micrometers, typically no greater than 10micrometers, and more typically no greater than 5 micrometers asmeasured using, for example, a sedimentation particle size analyzer.Suitable FAS glasses will be familiar to those skilled in the art, andare available from a wide variety of commercial sources, and many arefound in currently available glass ionomer cements such as thosecommercially available under the trade designations VITREMER, VITREBOND,RELY X LUTING CEMENT, RELY X LUTING PLUS CEMENT, PHOTAC-FIL QUICK,KETAC-MOLAR, and KETAC-FIL PLUS (3M ESPE Dental Products, St. Paul,Minn.), FUJI II LC and FUJI IX (G-C Dental Industrial Corp., Tokyo,Japan) and CHEMFIL Superior (Dentsply International, York, Pa.).Mixtures of fillers can be used if desired.

Other suitable fillers are disclosed in U.S. Pat. No. 6,387,981 (Zhanget al.) and U.S. Pat. No. 6,572,693 (Wu et al.) as well as PCTInternational Publication Nos. WO 01/30305 (Zhang et al.), U.S. Pat. No.6,730,156 (Windisch et al.), WO 01/30307 (Zhang et al.), and WO03/063804 (Wu et al.). Filler components described in these referencesinclude nanosized silica particles, nanosized metal oxide particles, andcombinations thereof. Nanofillers are also described in U.S. Pat. No.7,090,721 (Craig et al.), U.S. Pat. No. 7,090,722 (Budd et al.) and U.S.Pat. No. 7,156,911; and U.S. Pat. No. 7,649,029 (Kolb et al.).

Examples of suitable organic filler particles include filled or unfilledpulverized polycarbonates, polyepoxides, poly(meth)acrylates and thelike. Commonly employed dental filler particles are quartz, submicronsilica, and non-vitreous microparticles of the type described in U.S.Pat. No. 4,503,169 (Randklev).

Mixtures of these fillers can also be used, as well as combinationfillers made from organic and inorganic materials.

Fillers may be either particulate or fibrous in nature. Particulatefillers may generally be defined as having a length to width ratio, oraspect ratio, of 20:1 or less, and more commonly 10:1 or less. Fiberscan be defined as having aspect ratios greater than 20:1, or morecommonly greater than 100:1. The shape of the particles can vary,ranging from spherical to ellipsoidal, or more planar such as flakes ordiscs. The macroscopic properties can be highly dependent on the shapeof the filler particles, in particular the uniformity of the shape.

Micron-size particles are very effective for improving post-cure wearproperties. In contrast, nanoscopic fillers are commonly used asviscosity and thixotropy modifiers. Due to their small size, highsurface area, and associated hydrogen bonding, these materials are knownto assemble into aggregated networks.

In some embodiments, the dental composition preferably comprise ananoscopic particulate filler (i.e., a filler that comprisesnanoparticles) having an average primary particle size of less thanabout 0.100 micrometers (i.e., microns), and more preferably less than0.075 microns. As used herein, the term “primary particle size” refersto the size of a non-associated single particle. The average primaryparticle size can be determined by cutting a thin sample of hardeneddental composition and measuring the particle diameter of about 50-100particles using a transmission electron micrograph at a magnification of300,000 and calculating the average. The filler can have a unimodal orpolymodal (e.g., bimodal) particle size distribution. The nanoscopicparticulate material typically has an average primary particle size ofat least about 2 nanometers (nm), and preferably at least about 7 nm.Preferably, the nanoscopic particulate material has an average primaryparticle size of no greater than about 75 nm, and more preferably nogreater than about 20 nm in size. The average surface area of such afiller is preferably at least about 20 square meters per gram (m²/g),more preferably, at least about 50 m²/g, and most preferably, at leastabout 100 m²/g.

In some preferred embodiments, the dental composition comprises silicananoparticles. Suitable nano-sized silicas are commercially availablefrom Nalco Chemical Co. (Naperville, Ill.) under the product designationNALCO COLLOIDAL SILICAS. For example, preferred silica particles can beobtained from using NALCO products 1040, 1041, 1042, 1050, 1060, 2327and 2329.

Silica particles are preferably made from an aqueous colloidaldispersion of silica (i.e., a sol or aquasol). The colloidal silica istypically in the concentration of about 1 to 50 weight percent in thesilica sol. Colloidal silica sols that can be used are availablecommercially having different colloid sizes, see Surface & ColloidScience, Vol. 6, ed. Matijevic, E., Wiley Interscience, 1973. Preferredsilica sols for use making the fillers are supplied as a dispersion ofamorphous silica in an aqueous medium (such as the Nalco colloidalsilicas made by Nalco Chemical Company) and those which are low insodium concentration and can be acidified by admixture with a suitableacid (e.g. Ludox colloidal silica made by E. I. Dupont de Nemours & Co.or Nalco 2326 from Nalco Chemical Co.).

Preferably, the silica particles in the sol have an average particlediameter of about 5-100 nm, more preferably 10-50 nm, and mostpreferably 12-40 nm. A particularly preferred silica sol is NALCO™ 1042or 2327.

In some embodiments, the dental composition comprises zirconiananoparticles. Suitable nano-sized zirconia nanoparticles can beprepared using hydrothermal technology as described in U.S. Pat. No.7,241,437 (Davidson et al.).

In some embodiments, lower refractive index (e.g. silica) nanoparticlesare employed in combination with high refractive index (e.g. zirconia)nanoparticles in order to index match (refractive index within 0.02) thefiller to the refractive index of the polymerizable resin.

In some embodiments, the nanoparticles are in the form of nanoclusters,i.e. a group of two or more particles associated by relatively weakintermolecular forces that cause the particles to clump together, evenwhen dispersed in a hardenable resin.

Preferred nanoclusters can comprise a substantially amorphous cluster ofnon-heavy (e.g. silica) particles, and amorphous heavy metal oxide (i.e.having an atomic number greater than 28) particles such as zirconia. Theprimary particles of the nanocluster preferably have an average diameterof less than about 100 nm. Suitable nanocluster fillers are described inU.S. Pat. No. 6,730,156 (Windisch et al.); incorporated herein byreference.

In some preferred embodiments, the dental composition comprisesnanoparticles and/or nanoclusters surface treated with an organometalliccoupling agent to enhance the bond between the filler and the resin. Theorganometallic coupling agent may be functionalized with reactive curinggroups, such as acrylates, methacrylates, vinyl groups and the like andmay comprise silane, zirconate or titanate coupling agents. Preferredcoupling agents include gamma-methacryloxypropyltrimethoxysilane,gamma-mercaptopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane,and the like.

Suitable copolymerizable or reactive organometallic compounds may havethe general formulas: CH₂═C(R²²)—R²¹Si(OR)_(n)R_(3-n) orCH₂═C(R²²)—C═OOR²¹Si(OR)_(n)R_(3-n); wherein R is an C₁-C₄ alkyl, R²¹ isa divalent organic heterohydrocarbyl linking group, preferably alkylene;R²² is H or C1-C4 alkyl; and n is from 1 to 3. Preferred coupling agentsinclude gamma-methacryloxypropyltrimethoxysilane,gamma-mercaptopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane,and the like.

In some embodiments, the silica particulate filler may be surfacemodified by an addition-fragmentation agent, such as are described inApplicant's copending applications U.S. 2012/050718 (Joly et al.) andU.S. Ser. No. 61/725,077 (Joly et al.) each incorporated herein byreference.

In some embodiments, the disclosure provides a universal restorativecomposite comprising:

a) 15-30 wt. % of a curable dental resin comprising at least twopolymerizable, ethylenically unsaturated groups;b) 70-85 wt. % of an inorganic filler, preferably a surface modifiedfiller;c) 0.1 to 10 wt. % by weight of the addition-fragmentation agent,relative to 100 parts by weight of a) and b), said curable compositionfurther comprising an initiator and <2%, stabilizers, pigments, etc.

In some embodiments, the disclosure provides a flowable restorative(flowable) composite comprising:

a) 25-50 wt. % of a curable dental resin comprising at least twopolymerizable, ethylenically unsaturated groups;b) 30-75 wt. % of an inorganic filler, preferably a surface modifiedfiller;c) 0.1 to 10 parts by weight of the addition-fragmentation agent,relative to 100 parts by weight of a) and b), said curable compositionfurther comprising an initiator and <2% initiators, stabilizers,pigments, etc.

In some embodiments, the disclosure provides a resin modifiedglass-ionomer adhesive comprising:

-   -   a) 10-25 wt. % of a partially (meth)acrylated poly(meth) acrylic        acid, which includes acrylic acids such as itaconic acid;    -   b) 5-20 wt. % of a hydroxyalkyl (meth)acrylate;    -   c) 30-60 wt. % of fluoroaluminosilicate (FAS) acid reactive        glass    -   d) 0-20 wt. % non-acid reactive fillers, preferably        surface-treated;    -   e) 10-20 wt. % water; and    -   f) 0.1 to 10 wt. % of the addition-fragmentation agent, relative        to 100 parts by weight of a) and b),    -   g) said curable composition further comprising an initiator and        <2% stabilizers, pigments.

Preferably the floroaluminosilicate is a silane methacrylatesurface-treated floroaluminosilicate.

In some embodiments, the disclosure provides a dental adhesivecomprising:

a) 30-80 wt. % mono (meth)acrylate monomers;b) 1-10 wt. % polyfunctional (meth)acrylate monomers;c) 5-60 wt. % monomers having a acid-functional group (includingphosphate, phosphonate, carboxylate, sulfonic acids)d) 0-10, preferably 1-10 wt. % poly(meth)acrylic acid methacrylatemonomers;e) 0.1 to 10 wt. % of the addition-fragmentation agent, relative to 100parts by weight of a) to d);f) an initiator,g) 0-30 wt. % inorganic filler, preferably surface modified, relative to100 parts by weight of a) to d);h) 0 to 25 wt. % solvent relative to 100 parts by weight of a) to d);i) 0 to 25 wt. % water relative to 100 parts by weight of a) to d); and<2% stabilizers, pigments.

In some embodiments, the dental compositions can have an initial colordifferent than the cured dental structures. Color can be imparted to thecomposition through the use of a photobleachable or thermochromic dye.As used herein, “photobleachable” refers to loss of color upon exposureto actinic radiation. The composition can include at least 0.001 wt. %photobleachable or thermochromic dye, and typically at least 0.002 wt. %photobleachable or thermochromic dye, based on the total weight of thecomposition. The composition typically includes at most 1 wt. %photobleachable or thermochromic dye, and more typically at most 0.1 wt.% photobleachable or thermochromic dye, based on the total weight of thecomposition. The amount of photobleachable and/or thermochromic dye mayvary depending on its extinction coefficient, the ability of the humaneye to discern the initial color, and the desired color change. Suitablethermochromic dyes are disclosed, for example, in U.S. Pat. No.6,670,436 (Burgath et al.).

For embodiments including a photobleachable dye, the color formation andbleaching characteristics of the photobleachable dye varies depending ona variety of factors including, for example, acid strength, dielectricconstant, polarity, amount of oxygen, and moisture content in theatmosphere. However, the bleaching properties of the dye can be readilydetermined by irradiating the composition and evaluating the change incolor. The photobleachable dye is generally at least partially solublein a hardenable resin.

Photobleachable dyes include, for example, Rose Bengal, MethyleneViolet, Methylene Blue, Fluorescein, Eosin Yellow, Eosin Y, Ethyl Eosin,Eosin bluish, Eosin B, Erythrosin B, Erythrosin Yellowish Blend,Toluidine Blue, 4′,5′-Dibromofluorescein, and combinations thereof.

The color change can be initiated by actinic radiation such as providedby a dental curing light which emits visible or near infrared (IR) lightfor a sufficient amount of time. The mechanism that initiates the colorchange in the compositions may be separate from or substantiallysimultaneous with the hardening mechanism that hardens the resin. Forexample, a composition may harden when polymerization is initiatedchemically (e.g., redox initiation) or thermally, and the color changefrom an initial color to a final color may occur subsequent to thehardening process upon exposure to actinic radiation.

Optionally, compositions may contain solvents (e.g., alcohols (e.g.,propanol, ethanol), ketones (e.g., acetone, methyl ethyl ketone), esters(e.g., ethyl acetate), other nonaqueous solvents (e.g.,dimethylformamide, dimethylacetamide, dimethylsulfoxide,1-methyl-2-pyrrolidinone)), and water.

If desired, the compositions can contain additives such as indicators,dyes, pigments, inhibitors, accelerators, viscosity modifiers, wettingagents, buffering agents, radical and cationic stabilizers (for exampleBHT,), and other similar ingredients that will be apparent to thoseskilled in the art.

Additionally, medicaments or other therapeutic substances can beoptionally added to the dental compositions. Examples include, but arenot limited to, fluoride sources, whitening agents, anticaries agents(e.g., xylitol), calcium sources, phosphorus sources, remineralizingagents (e.g., calcium phosphate compounds), enzymes, breath fresheners,anesthetics, clotting agents, acid neutralizers, chemotherapeuticagents, immune response modifiers, thixotropes, polyols,anti-inflammatory agents, antimicrobial agents (in addition to theantimicrobial lipid component), antifungal agents, agents for treatingxerostomia, desensitizers, and the like, of the type often used indental compositions. Combinations of any of the above additives may alsobe employed. The selection and amount of any one such additive can beselected by one of skill in the art to accomplish the desired resultwithout undue experimentation.

The curable dental composition can be used to treat an oral surface suchas tooth, as known in the art. In some embodiments, the compositions canbe hardened by curing after applying the dental composition. Forexample, when the curable dental composition is used as a restorativesuch as a dental filling, the method generally comprises applying thecurable composition to an oral surface (e.g. cavity); and curing thecomposition. In some embodiments, a dental adhesive may be applied priorto application of the curable dental restoration material describedherein. Dental adhesives are also typically hardened by curingconcurrently with curing the highly filled dental restorationcomposition. The method of treating an oral surface may compriseproviding a dental article and adhering the dental article to an oral(e.g. tooth) surface.

In other embodiments, the compositions can be cured into dental articlesprior to applying. For example, a dental article such as a crown may bepre-formed from the curable dental composition described herein. Dentalcomposite (e.g. crowns) articles can be made from the curablecomposition described herein by casting the curable composition incontact with a mold and curing the composition. Alternatively, dentalcomposites or articles (e.g. crowns) can be made by first curing thecomposition forming a mill blank and then mechanically milling thecomposition into the desired article.

Another method of treating a tooth surface comprises providing a dentalcomposition as described herein wherein the composition is in the formof a (partially cured) curable, self-supporting, malleable structurehaving a first semi-finished shape; placing the curable dentalcomposition on a tooth surface in the mouth of a subject; customizingthe shape of the curable dental composition; and hardening the curabledental composition. The customization can occur in the patient's mouthor on a model outside the patient mouth such as described in U.S. Pat.No. 7,674,850 (Karim et al.); incorporated herein by reference.

EXAMPLES

As used herein, the term AFM refers to addition fragmentation agents.Unless otherwise specified, all percentages are by weight.

Test Methods Depth of Cure Test Method (DOC)

The depth of cure (DOC) was measured for a test sample composition aftercuring. A test fixture with an open 8 millimeter stainless steel moldcavity was placed on a polyester film and filled with the samplecomposition. A second polyester film placed atop the resin and fixturewas pressed to provide a level surface on the composition. The filledtest fixture was placed on a white background surface and thecomposition was irradiated for 20 seconds using a dental curing light(3M Dental Products Curing Light 2500 or 3M ESPE Elipar FreeLight2, 3MESPE Dental Products). After curing, the sample was removed from themold and the uncured resin was gently removed, e.g., gently scrapingmaterials from the bottom of the sample which was the side that was notirradiated with the curing light. The thickness of the remaining curedmaterial was measured. The reported depths are the actual curedthickness in millimeters divided by 2.

Stress Test Method (Cusp Deflection)

This test measures the stress development during the curing process. Atest fixture was prepared by machining a slot into a rectangular 15 mm×8mm×8 mm aluminum block. The slot was 8 mm long, 2.5 mm deep, and 2 mmacross, and was located 2 mm from an edge, thus forming a 2 mm widealuminum cusp adjacent to a 2 mm wide cavity containing the testcompositions. A linear variable displacement transducer (Model GT 1000,used with an E309 analog amplifier (RDP Electronics, United Kingdom) waspositioned to measure the displacement of the cusp tip as the dentalcomposition was photocured at room temperature. Prior to testing, theslot in the aluminum block was sandblasted using Rocatec Plus SpecialSurface Coating Blasting Material (3M ESPE), treated with RelyX CeramicPrimer (3M ESPE), and finally treated with a dental adhesive, Adper EasyBond (3M ESPE).

The slot was fully packed with the composition, which equaledapproximately 100 mg of material. The material was irradiated for 1minute with a dental curing lamp (Elipar S-10, 3M ESPE) positionedalmost in contact (less than 1 mm) with the material in the slot. Thedisplacement of the cusp in microns was recorded 9 minutes after thelamp was extinguished.

Refractive Indices were measured at room temperature on a refractometermanufactured by Bausch & Lomb (Rochester, N.Y., USA) Cat. No. 33.46.10.

Materials.

Commercial reagents were used as received. When not specified, reagentswere obtained from Sigma Aldrich or EMD.

-   -   2-Biphenyl isocyanate—Sigma Aldrich, St. Louis, Mo.    -   2-Biphenyl carboxylic acid—Sigma Aldrich, St. Louis, Mo.    -   2-Naphthoyl chloride—Sigma Aldrich, St. Louis, Mo.    -   4-(Dimethylamino)pyridine—Sigma Aldrich, St. Louis, Mo.        4-Methacryloxyethyl trimellitic anhydride, Polysciences, Inc.,        Warrington, Pa., USA    -   AFM-1—prepared as described in U.S. Patent Application No.        2012-0208965, “Addition-Fragmentation Agents” (67046US003)    -   BisGMA—(2,2-Bis[4-(2-hydroxy-3-methacryloyloxy-propoxy)phenyl]propane,        Sigma Aldrich, St. Louis, Mo., USA    -   CPQ—camphorquinone, Sigma Aldrich, St. Louis, Mo., USA    -   Dichloromethane—EMD Chemicals Inc.; Gibbstown, N.J., USA    -   DPIHFP—Diphenyliodonium hexafluorophosphate (≧98%), Sigma        Aldrich, St. Louis, Mo.    -   EDMAB—Ethyl 4-N,N-dimethylamino benzoate, Sigma Aldrich, St.        Louis, Mo., USA    -   Filler A—filler prepared according to Example 1 of U.S. Pat. No.        4,503,169, incorporated herein in its entirety by reference    -   HEMA—Hydyroxyethyl methacrylate, Sigma Aldrich, St. Louis, Mo.,        USA    -   MEHQ—Sigma Aldrich, St. Louis, Mo. MHP—6-methacryloyloxyhexyl        phosphate—compound preparation described in U.S. Patent        Publication No. 2009-0011388 (Craig, et al.)    -   Oxalyl chloride—Sigma Aldrich, St. Louis, Mo.    -   Sodium bicarbonate—Sigma Aldrich; St. Louis, Mo.    -   Triethylamine—Sigma Aldrich, St. Louis, Mo.    -   UDMA—Rohamere™ 6661-0 (diurethane dimethacrylate, CAS No. 41        137-60-4), Rohm Tech, Inc., Malden, Mass.    -   YbF₃—Ytterbium(III) fluoride, Sigma Aldrich, St. Louis, Mo.

Instrumentation

Nuclear magnetic resonance spectra (proton—¹H NMR) were analyzed andrecorded using an NMR spectrometer (UltraShield™ Plus 400 MHz NMRspectrometer; Bruker Corporation; Billerica, Mass.).

Example 1

A solution of oxalyl chloride (16.8 mmol, 2.13 g) in 10 mLdichloromethane was added dropwise via an addition funnel to a solutionof 2-biphenyl carboxylic acid (16.8 mmol, 3.33 g) in 30 mLdichloromethane under a nitrogen atmosphere in a 3-neck flask equippedwith a magnetic stir bar, and stirred at room temperature for 3 hours.The solvents were removed under reduced pressure, and the residue wasdissolved in 30 mL of dichloromethane. A solution of AFM-1 (8.00 mmol,3.65 g), 4-(dimethylamino)pyridine (0.80 mmol, 98 mg), and triethylamine(24.0 mmol, 2.43 g) in 30 mL dichloromethane was added dropwise via theaddition funnel under a nitrogen atmosphere and stirred at roomtemperature overnight. The mixture was then washed sequentially with 1NHCl, distilled water, sat. aq. sodium bicarbonate, and brine.Approximately 250 ppm MEHQ was added and the organic layer was driedover magnesium sulfate, filtered, and concentrated under reducedpressure. Air was bubbled through the resultant syrup for 24 hours toprovide 6.26 g of a thick, clear, pale yellow syrup (96% of theoreticalyield). ¹H NMR evaluation of this material (CDCl₃, 500 MHz) wasconsistent with the structure of AFM-A, although multiple isomers areevident.

The refractive index was 1.5944.

Example 2

A 250 ml 3-neck round-bottomed flask equipped with a magnetic stir bar,two plastic caps, and a pressure-equalizing addition funnel was chargedwith AFM-1 (5.00 g, 10.95 millimole) and dichloromethane (20 mL). Two 16gauge needles were inserted into the plastic caps to vent the reactionto air. With stirring, the homogeneous solution was cooled to 0° C. inan ice water batch. Triethylamine (5.40 mL, 3.92 g, 38.7 mmol) and4-(dimethylamino)pyridine (0.401 g, 3.29 mmol) were added to thereaction mixture and the valve in the addition funnel was closed.2-Naphthoyl chloride (4.28 g, 22.4 mmol) and dichloromethane (45 mL)were added to the addition funnel and the addition funnel was sealedwith a plastic cap. The reaction apparatus was gently shaken to mix anddissolve the 2-naphthoyl chloride. The solution in the addition funnelwas added to the reaction mixture dropwise over approximately 30minutes. The reaction was allowed to slowly warm to room temperatureovernight. After 72 hours, the reaction mixture was transferred to a 500mL separatory funnel and diluted with dichloromethane to approximately175 mL total volume. The dichloromethane solution was washed withdeionized water (1×200 mL), 1N HCl_(aq) (2×200 mL), deionized water(1×150 mL), 1N NaOH_(aq) (3×150 mL), deionized water (1×150 mL), andsaturated NaCl_(aq) (1×200 mL). The organic solution was then dried oversodium sulfate for approximately 1 hour. Next, the organic solution wasvacuum filtered and concentrated in vacuo to provide a very pale yellowoil. The concentrated sample was dissolved in dichloromethane (25 mL)and 2,6-ditertbutyl-4-methoxy phenol (0.003 g) was added. The solutionwas transferred to an approximately 25 mL amber bottle and was dried bygently bubbling a stream of air through the material. ¹H NMR analysiswas consistent with the structure of AFM-B as a mixture of isomers.AFM-B (7.52 g, 9.83 mmole, 90% of theoretical yield) was obtained as avery viscous, very pale yellow material.

The refractive index was 1.5952.

Example 3

An approximately 20 ml clear glass vial was charged with AFM-1 (2.00 g,4.38 mmole) and 2-biphenyl isocyanate (1.5 mL, 1.71 g, 8.77 mmol). Amagnetic stir bar was added to the vial and it was loosely capped with aTeflon-lined plastic cap to allow exchange with ambient atmosphere. Withstirring, the mixture was heated to 70° C. in an oil bath. After 24hours, the reaction was cooled to room temperature. ¹H NMR analysis wasconsistent with the structure of AFM-C as a mixture of isomers. AFM-C(3.68 g, 4.35 mmole, 99% of theoretical yield) was obtained as a clear,almost colorless glass-like material.

The refractive index was 1.5971.

Examples 4-8 Comparative Example C1

Paste compositions suitable for dental resins were prepared by mixingthe compositions shown in Table 1 to form uniform dispersions withAFM-A. Amounts shown in the tables are in weight percent. Thecompositions were tested according to the test methods described abovefor the depth of cure (ISO DOC) in millimeters (mm) Results are shown inTable 1.

Example C1 was prepared and tested in the same manner except that no AFMwas added.

TABLE 1 Example C1 4 5 6 7 8 BisGMA 17.4 16.53 15.66 14.79 13.92 13.05HEMA 11.6 11.02 10.44 9.86 9.28 8.70 MHP 10.0 9.50 9.00 8.50 8.00 7.50CPQ 0.32 0.30 0.29 0.27 0.26 0.24 EDMAB 0.48 0.46 0.43 0.41 0.38 0.36DPIPF6 0.20 0.19 0.18 0.17 0.16 0.15 AFM-A 0 2.0 4.0 6.0 8.0 10.0FillerA 60.0 60.0 60.0 60.0 60.0 60.0 Total 100.0 100.0 100.0 100.0100.0 100.0 DOC 3.42 3.28 3.25 3.17 3.18 3.20

Examples 9-18 and Comparative Examples C2 and C3

Compositions were prepared and tested as described above for Examples1-8, except that AFM-B (Examples 9-13) or AFM-C (Examples 14-18) wereused instead of AFM-A. Amounts of other materials for each amount of AFMremained the same for all three AFMs.

Comparative examples C2 and C3 were the same compositions prepared indifferent batches with no AFMs.

The compositions were tested as described above for depth of cure.Additionally, stress, indicated by cusp deflection (cusp deft), wasmeasured for Examples 14-18 and C3. Results are shown in Tables 2 and 3for AFM-B and AFM-C, respectively.

TABLE 2 Example C2 9 10 11 12 13 AFM-B None 2% 4% 6% 8% 10% ISO DOC 3.423.34 3.30 3.45 3.49 3.71

TABLE 3 Example C3 14 15 16 17 18 AFM-C None 2% 4% 6% 8% 10% DOC 3.003.18 3.35 3.42 3.48 3.56 Cusp defl. (microns) −6.96 −5.34 −4.03 −2.76−1.65 −1.06The present disclosure provides the following illustrative embodiments:1. An addition fragmentation agent of the formula:

-   -   wherein    -   R¹ is each independently a (hetero)alkyl group or a (hetero)aryl        group Y is −O—. —S—, —O—CO—, O—CO—NH—, —N—CO—, or —NR⁴—, where        R⁴ is H or C₁-C₄ alkyl;    -   each X¹ is independently —O— or —NR⁴—, where R⁴ is H or C₁-C₄        alkyl, and    -   n is 0 or 1;    -   m is each independently 1 or 2,    -   R² is alkyl, aryl, a high refractive index group, or and        ethylenically unsaturated polymerizable group;    -   at least one of said R² groups is a high refractive index group;    -   at least one of said R² groups comprises an ethylenically        unsaturated, polymerizable group; and    -   said addition-fragmentation agent having a refractive index of        ≧1.50.        2. The addition-fragmentation agent of embodiment 1, wherein        said ethylenically unsaturated, polymerizable group is a        (meth)acryloyl group.        3. The addition-fragmentation agent of any of the previous        embodiments wherein at least two of said R² groups is a high        refractive index group.        4. The addition-fragmentation agent of embodiment 1, wherein at        least two of said R² groups is a (meth)acryloyl group.        5. The addition-fragmentation agent of any of the previous        embodiments, wherein at least one of said R¹—Y—R² groups is of        the formula:

wherein

R⁴ is H or C₁-C₄ alkyl;

X¹ is independently —O— or —NR⁴—, where R⁴ is H or C₁-C₄ alkyl; and

t is 2 to 10, said —(C_(t)H_(2t))— group optionally substituted by ahydroxy.

6. The addition-fragmentation agent of any of the previous embodiments,wherein the high refractive index group is selected from benzyl, 2-, 3-,and 4-biphenyl, 1-, 2, 3-, 4-, and 9-fluorenyl,4-(1-methyl-1-phenethyl)phenoxyethyl; phenylthio; 1-, 2-, 3- and4-napthyl, 1- and 2-naphthylthio; 2,4,6-tribromophenoxy;2,4-dibromophenoxy; 2-bromophenoxy; 1-, and 2-naphthyloxy; 3-phenoxy-;2-, 3- and 4-phenylphenoxy; 2,4-dibromo-6-sec-butylphenyl;2,4-dibromo-6-isopropylphenyl; 2,4-dibromophenyl; pentabromobenzyl andpentabromophenyl.7. The addition-fragmentation agent of any of the previous embodimentsof the formula:

-   -   wherein    -   R^(RI) comprises a high refractive index group;    -   R^(polmn) comprises an ethylenically unsaturated, polymerizable        group;    -   R³² is either R^(RI) or R^(polmn);    -   R³³ is alkyl or aryl, an ethylenically unsaturated polymerizable        group or a high refractive index group;    -   Y is −O—. —S—, —O—CO—, O—CO—NH—, —N—CO—, or —NR⁴—, where R⁴ is H        or C₁-C₄ alkyl;    -   each X¹ is independently —O— or —NR⁴—, where R⁴ is H or C₁-C₄        alkyl, and    -   n is 0 or 1;    -   each o is independently 1 or 2,    -   each p is independently 0 or 1,    -   with the proviso that compound Ia comprises at least one        ethylenically unsaturated polymerizable group and at least one        high refractive index group.        8. A polymerizable composition comprising the        addition-fragmentation agent of any of the previous embodiments,        at least one free-radically polymerizable monomer, and an        initiator.        9. The polymerizable composition of embodiment 8 comprising:    -   a) 85 to 100 parts by weight of an (meth)acrylic acid ester;    -   b) 0 to 15 parts by weight of an acid functional ethylenically        unsaturated monomer;    -   c) 0 to 10 parts by weight of a non-acid functional,        ethylenically unsaturated polar monomer;    -   d) 0 to 5 parts vinyl monomer; and    -   e) 0 to 5 parts of a multifunctional (meth)acrylate;    -   based on 100 parts by weight total monomer a) to e), and    -   f) 0.1 to 10 parts by weight of the addition-fragmentation        agent, based on 100 parts by weight of a) to e).        10. The polymerizable composition of embodiment 9 further        comprising 0.01 to 5 parts of a multifunctional (meth)acrylate.        11. The polymerizable composition of any of embodiments 8-10        further comprising a photoinitiator.        12. The polymerizable composition of any of embodiments 8-10        wherein the initiator is a thermal initiator.        13. The polymerizable composition of any of embodiments 8-12        further comprising an inorganic filler.        14. The polymerizable composition of embodiment 13 wherein the        filler is a surface-modified silica filler.        15. An article comprising a layer of the polymerizable        composition of any of embodiments 8-14 on a substrate.        16. An article comprising the cured polymerizable composition of        any of embodiments 8-14 on a substrate.        17. A method of bonding two substrates together comprising the        steps of coating the polymerizable composition of any of        embodiments 8-14 to a surface of one or both substrates,        contacting the coated surfaces, optionally with pressure, and        curing the polymerizable compositions.        18. A method of bonding two substrates together comprising the        steps of coating the polymerizable composition of any of        embodiments 8-14 to a surface of one or both substrates, wherein        the coating of polymerizable composition is at least partially        cured, contacting the coated surfaces optionally with pressure,        and further curing the polymerizable compositions if necessary.        19. A hardcoat composition comprising one or more        multifunctional (meth)acrylate monomers or (meth)acrylate        oligomers, and the addition-fragmentation agent of any of        embodiments 1-7.        20. The hardcoat composition of embodiment 19 comprising:    -   a) 0.1-10 wt. % of the addition fragmentation agent;    -   b) 20-80 wt. % of multifunctional (meth)acrylate monomers and/or        multifunctional (meth)acrylate oligomers,    -   c) 0 to 25 wt. % range of (meth)acrylate diluent, (0-25 wt. %);        and    -   d) 20 to 75 wt. % of silica.        21. A curable dental composition comprising:    -   a) at least one dental resin comprising at least two        ethylenically unsaturated group;    -   b) the addition-fragmentation agent of any of claims 1-7; and    -   c) optionally an inorganic oxide filler;    -   said addition-fragmentation agent having a refractive index of        ≧1.50.        22. The dental composition of claim 21 wherein the dental resin        comprises an aromatic monomer having a refractive index of at        least 1.50.        23. The dental composition of claim 21 wherein the dental resin        is a low volume shrinkage resin.        24. The dental composition of any of the preceding claims 21-23        further comprising a nanoparticle inorganic oxide filler.        25. The dental composition of claim 24 wherein the inorganic        oxide nanoparticles comprise silica, zirconia, or mixtures        thereof.        26. The dental composition of any of claims 21-25 comprising a        surface modified inorganic oxide filler.        27. A method of treating a tooth surface, the method comprising    -   a) providing a curable dental resin of any of claims 21-26;    -   b) placing the dental composition on a tooth surface in the        mouth of a subject; and    -   c) hardening the hardenable dental composition.

1. An addition fragmentation agent of the formula:

wherein R¹ is each independently a (hetero)alkyl group or a (hetero)arylgroup Y is —O—. —S—, —O—CO—, O—CO—NH—, —N—CO—, or —NR⁴—, where R⁴ is Hor C1-C4 alkyl; each X¹ is independently —O— or —NR⁴—, where R⁴ is H orC1-C4 alkyl, and n is 0 or 1; m is each independently 1 or 2, R² isalkyl, aryl, a high refractive index group, or and ethylenicallyunsaturated polymerizable group; at least two of said R² groups is ahigh refractive index group; at least two of said R² groups comprises anethylenically unsaturated, polymerizable group; and saidaddition-fragmentation agent having a refractive index of ≧1.50.
 2. Theaddition-fragmentation agent of claim 1, wherein said ethylenicallyunsaturated, polymerizable group is a (meth)acryloyl group.
 3. Theaddition-fragmentation agent of claim 1 wherein at least two of said R²groups is a high refractive index group.
 4. The addition-fragmentationagent of claim 1, wherein at least two of said R² groups is a(meth)acryloyl group.
 5. The addition-fragmentation agent of claim 4,wherein at least one of said R¹—Y—R² groups is of the formula:

wherein R⁴ is H or C1-C4 alkyl; X¹ is independently —O— or —NR⁴—, whereR⁴ is H or C1-C4 alkyl; and t is 2 to 10, said —(C_(t)H_(2t))— groupoptionally substituted by a hydroxy.
 6. The addition-fragmentation agentof claim 1, wherein the high refractive index group is selected frombenzyl, 2-, 3-, and 4-biphenyl, 1-, 2, 3-, 4-, and 9-fluorenyl,4-(1-methyl-1-phenethyl)phenoxyethyl; phenylthio; 1-, 2-, 3- and4-napthyl, 1- and 2-naphthylthio; 2,4,6-tribromophenoxy;2,4-dibromophenoxy; 2-bromophenoxy; 1-, and 2-naphthyloxy; 3-phenoxy-;2-, 3- and 4-phenylphenoxy; 2,4-dibromo-6-sec-butylphenyl;2,4-dibromo-6-isopropylphenyl; 2,4-dibromophenyl; pentabromobenzyl andpentabromophenyl.
 7. The addition-fragmentation agent of claim 1 of theformula:

wherein R^(RI) comprises a high refractive index group; R^(polmn)comprises an ethylenically unsaturated, polymerizable group; R³² iseither R^(RI) or R^(polmn); R³³ is alkyl or aryl, an ethylenicallyunsaturated polymerizable group or a high refractive index group; Y is−O—. —S—, —O—CO—, O—CO—NH—, —N—CO—, or —NR⁴—, where R⁴ is H or C1-C4alkyl; each X¹ is independently —O— or —NR⁴—, where R⁴ is H or C1-C4alkyl, and n is 0 or 1; each o is independently 1 or 2, each p isindependently 0 or 1, with the proviso that compound Ia comprises atleast one ethylenically unsaturated polymerizable group and at least onehigh refractive index group.
 8. A polymerizable composition comprisingthe addition-fragmentation agent of claim 1, at least one free-radicallypolymerizable monomer, and an initiator.
 9. The polymerizablecomposition of claim 8 comprising: a) 85 to 100 parts by weight of an(meth)acrylic acid ester; b) 0 to 15 parts by weight of an acidfunctional ethylenically unsaturated monomer; c) 0 to 10 parts by weightof a non-acid functional, ethylenically unsaturated polar monomer; d) 0to 5 parts vinyl monomer; and e) 0 to 5 parts of a multifunctional(meth)acrylate; based on 100 parts by weight total monomer a) to e), andf) 0.1 to 10 parts by weight of the addition-fragmentation agent, basedon 100 parts by weight of a) to e).
 10. The polymerizable composition ofclaim 9 further comprising 0.01 to 5 parts of a multifunctional(meth)acrylate.
 11. The polymerizable composition of claim 8 furthercomprising a photoinitiator.
 12. The polymerizable composition of claim8 wherein the initiator is a thermal initiator.
 13. The polymerizablecomposition of claim 8 further comprising an inorganic filler.
 14. Thepolymerizable composition of claim 13 wherein the filler is asurface-modified silica filler.
 15. An article comprising a layer of thepolymerizable composition of claim 8 on a substrate.
 16. An articlecomprising the cured polymerizable composition of claim 8 on asubstrate.
 17. A method of bonding two substrates together comprisingthe steps of coating the polymerizable composition of claim 8 to asurface of one or both substrates, contacting the coated surfaces,optionally with pressure, and curing the polymerizable compositions. 18.A method of bonding two substrates together comprising the steps ofcoating the polymerizable composition of claim 8 to a surface of one orboth substrates, wherein the coating of polymerizable composition is atleast partially cured, contacting the coated surfaces optionally withpressure, and further curing the polymerizable compositions ifnecessary.
 19. A hardcoat composition comprising one or moremultifunctional (meth)acrylate monomers or (meth)acrylate oligomers, andthe addition-fragmentation agent of claim
 1. 20. The hardcoatcomposition of claim 19 comprising: a) 0.1-10 wt. % of the additionfragmentation agent; b) 20-80 wt. % of multifunctional (meth)acrylatemonomers and/or multifunctional (meth)acrylate oligomers, c) 0 to 25 wt.% range of (meth)acrylate diluent, (0-25 wt. %); and d) 20 to 75 wt. %of silica.